At-Bias Extraction of Access Parasitic Resistances in AlGaN/GaN HEMTs: Impact on Device Linearity and Channel Electron Velocity

摘要

AlGaN/GaN high-electron mobility transistor “hot” parasitic source and drain resistances $R_{S,D}$ are determined under operating biases through wideband $S$-parameter measurements, without the use of “ColdFET” biasing conditions. Both $R_{S}$ and $R_{D}$ are found to increase dramatically over ColdFET values, both for biases approaching threshold and for open-channel conditions. Parasitic resistance values have a significant effect on the extracted small-signal equivalent circuit model elements, as well as on the apparent device linearity. The bias dependence of access resistances modifies the understanding of the transistor physical operation: A revised delay time analysis accounting for the bias dependence of parasitic resistances shows that the effective average electron velocity in the AlGaN/GaN two-dimensional electron-gas channel is approximately equal to $hbox{1.9} times hbox{10}^{7} hbox{cm/s}$. This new value of channel velocity is also consistent with the $C_{rm GS}/g_{rm MO}$ ratio obtained when the bias dependence of $R_{S}$ and $R_{D}$ is accounted for during the extraction of the transistor small-signal equivalent circuit model.