Electrical Characteristics of the 0.1 μm Gate Length Pseudomorphic High-Electron-Mobility Transistors with Low-Dielectric-Constant Benzo-Cyclo-Butene Passivations

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We examine the effects of thin-film passivation on the DC, RF and noise characteristics of 0.1-μm-gate-length pseudomorphic high-electron-mobility transistors (PHEMTs) when either conventional Si3N4 or low-dielectric-constant benzo-cyclo-butene (BCB) is used for the passivation layer. A significant shift in pinch-off voltage of ${\sim}{-0.4}$ V is observed from the PHEMTs after the Si3N4 passivation, whereas no such variation in DC parameters is observed in the case of BCB passivation. Noise figures of the devices are very stable after the BCB passivation and are only ${\sim}60$% of those in the case of Si3N4 passivation when measured at 55–62 GHz. Other RF parameters are not significantly affected by the passivation materials at a frequency of 50 GHz. We propose that the degradation in DC and noise characteristics can be due to the high density of surface states in the Si3N4 passivation layers; on the other hand, excellent stability in electrical characteristics in the BCB passivations can attribute to the minimized surface states in the passivation layer.
2003-12-15