RF Power Performance Evaluation of Surface Channel Diamond MESFET
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1203-J15-04
RF Power Performance Evaluation of Surface Channel Diamond MESFETs M. C. Rossi1, P. Calvani1, G. Conte1, V. Camarchia2, F. Cappelluti2, G. Ghione2, B. Pasciuto3, E. Limiti3, D. Dominijanni4 and E. Giovine4 1
Department of Electronic Engineering, Università di Roma Tre, Roma, Italy, Department of Electronics, Politecnico di Torino, Torino, Italy 3 Department of Electronic Engineering, Università di Tor Vergata, Roma, Italy 4 IFN-CNR, Roma, Italy 2
ABSTRACT Large-signal radiofrequency performances of surface channel diamond MESFET fabricated on hydrogenated polycrystalline diamond are investigated. The adopted device structure is a typical coplanar two-finger gate layout, characterized in DC by an accumulationlike behavior with threshold voltage Vt ~ 0-0.5 V and maximum DC drain current of 120 mA/mm. The best radiofrequency performances (in terms of fT and fmax) were obtained close to the threshold voltage. Realized devices are analyzed in standard class A operation, at an operating frequency of 2 GHz. The MESFET devices show a linear power gain of 8 dB and approximately 0.2 W/mm RF output power with 22% power added efficiency. An output power density of about 0.8 W/mm can be then extrapolated at 1 GHz, showing the potential of surface channel MESFET technology on polycrystalline diamond for microwave power devices. INTRODUCTION Diamond is, in principle, the highest performance widegap semiconductor, with outstanding electronic and thermal properties (high breakdown field, large carriers mobility and saturated velocity, thermal conductivity about 15 times larger than GaN and 50 than GaAs). This makes it an attractive material for high power radiofrequency (RF) and microwave electron devices, and a good candidate as a vacuum tube replacement in high power, high frequency applications like communications satellite and radar power stages. Although the properties of synthetic diamond have been known from many years (with the first diamond-based FETs demonstrated at the beginning of 90s) only recently significant technology advances in growth techniques for single-crystal and polycrystalline diamond have fostered the research on highperformance diamond electronics. Of particular significance is, at the present stage, the development of active devices on large area (4 inch wafers) polycrystalline diamond films, with 100-200 µm grain size, grown on different substrates, while single-crystal diamond substrates films are limited to smaller areas (a few square millimeters). 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 are being pursued in order to realize high speed power FETs [1], although the development of delta-channel FETs (based on boron delta-doped channels) is today well behind the one of H-terminated surfacechannel MESFETs which have demonstrated cut-off frequencies in
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