0.15 mu m gate-length double recess pseudomorphic HEMT with f/sub max/ of 350 GHz

The relative importance of f/sub t/ and f/sub max/ in millimeter-wave evaluation is discussed. Also presented is a study of the variation of C/sub gs/ (input capacitance), C/sub gd/ (gate-drain feedback capacitance), g/sub m/ (peak transconductance), and g/sub o/ (output conductance) with the distance, L/sub gd/, between the metal edge and the n/sup +/ cap layer on the drain side of the device in ultrashort-gate-length HEMT (high-electron-mobility transistors). For this study, a 0.15- mu m-gate-length, double-recess pseudomorphic HEMT was fabricated that exhibits a maximum frequency of oscillation, f/sub max/, of 350 GHz. This value is the highest f/sub max/ reported for any transistor. A very high C/sub gs//C/sub gd/ of 76 and a large voltage gain, g/sub m//g/sub o/ of 75 are observed in the device. These exceptional results are attained primarily by increasing L/sub gd/ to 2.3 times the gate length.<
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