Fabrication and Characterization of AlGaN/GaNOS High Electron Mobility Transistorsor High Frequency Applications
Date Issued
2009
Date
2009
Author(s)
Ming-Dung, Hsu
Abstract
We investigate the methods to improve the electric properties of AlGaN/GaN MOS High Electron Mobility Transistors (MOS-HEMTs). Using a transmission line model (TLM) analysis, we obtained an ohmic contact specific resistance of 6.654*10-6Ω-cm2 on the AlGaN/GaN samples patterned with a stack electrode of Ti/Al/Ti/Au (15nm/100nm/60nm/200nm) and annealed at 850℃ for 60s.We applied a new transistor structure with a dumb bell shape mesa and the photo-electro-chemical (PEC) method to form self passivation oxide layers on the surfaces of AlGaN/GaN. We note the device characteristic of saturation current increase from 950mA/mm to 1013mA/mm operated at VGS=1V and the Gm value increase from 181mS/mm to 191mS/mm for device of LG/WG=2μm/2μm.hen the PEC process was applied to the fabrication of AlGaN/GaN MOSFET, we can observe improvement in the direct current (DC) saturation current and the trans-conductance (Gm) measurement on transistors. By varying the drain-source LDS distance from 10 to 4μm while keep a fixed gate length LG=2μm, one not only can improve the DC properties but also increase the unit current gain cut off frequency (fT) from 12.6GHz to 25.6GHz. Furthermore, by reducing the device area to LDS=2μm to decrease the parasitic capacitance, the device cut-off frequency can be increase to 30.1GHz. Finally, from the DC and pulse current stressing experiment we denote that the AlGaN/GaN MOSFET encountered the PEC processing to provide surface passivation can exhibit improved performance against the current collapse effect.
Subjects
GaN
HEMT
Type
thesis
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