Gain and cut-off frequency analysis of multiple-gated AlGaAs/InGaAs HEMTs

A small signal analysis was performed on a specific 0.2 μm HEMT device to study the impact of multiple-gated layout towards the gain and cut-off frequency performance. The characterization process was using on-wafer measurement technique to AlGaAs/InGaAs HEMT devices which consisted of three types of layouts of various gate finger numbers and widths. The devices were biased at the optimum basing voltage obtained from DC characterization performed previously. From the result, it was observed that the device with higher number of gates exhibited higher gain only at low frequency, while at higher frequency the gain dropped significantly. This significant drop in gain was due to the increase of the gate-source capacitance in the device, thus leading to a reduction of the device cut-off frequency. The experimental findings were strongly supported by simulation which was based on related theory on the layout dimension contribution.