DC and RF performance of surface channel MESFETs on H-terminated polycrystalline diamond

DC and RF performance of submicron gate-length metal-semiconductor field effect transistors (MESFETs) fabricated on hydrogen-terminated polycrystalline diamond is investigated in detail for different material electronic quality (grain size in the range 100-200 mu m) and device geometry (drain-source channel length in the range 1-3 mu m). DC characteristics appear almost independent of both properties, giving maximum drain-source current values in the range 120-140 mA/mm in MESFETs having same gate length (0.2 mu m) and gate width (25 mu m). The layer properties underneath the hydrogenated surface seem then to affect the DC behaviour to a lesser extent when the same hydrogenation procedure is used. At variance, the electronic quality of diamond layers employed for MESFETs realization largely affects the RF performance, resulting into a low oscillation frequency f(max) for a MESFET realized by a self-aligned process (1 mu m drain-source channel length) onto low quality diamond polycrystalline film. Such a performance improves to f(max) = 35 GHz for devices realized onto large grain polycrystalline diamond, although fabricated without self-aligned gate procedure (3 mu m drain-source channel length). These findings are discussed in terms of different roles played by surface hydrogenation, device geometry detail and electronic quality of the polycrystalline diamond substrate for MESFET realization. (C) 2009 Elsevier B.V. All rights reserved.