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

摘要

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.