450 GHz amplifier MMIC in 50 nm metamorphic HEMT technology

We present a passivated 50 nm gate length metamorphic high electron mobility transistor (mHEMT) technology optimized for the successful fabrication of submillimeter-wave MMICs. A BCB based planarization process is used for placing a second 450 nm wide gate head, which is defined by optical lithography, on top of a 50 nm e-beam written T-gate. Due to the very low intrinsic resistances of the realized mHEMT devices an extrinsic maximum transconduction g_m,max of 2100 mS/mm was achieved together with an maximum drain current I_D,max of 1300 mA/mm. Furthermore, transit frequencies f_T and f_max of 370 and 670 GHz were extrapolated. The f_max extrapolation is based on measured S-parameters up to 220 GHz and compared with the small signal model used for circuit design on the 50 nm mHEMT process. The presented transistor technology was used to fabricate a four-stage common source amplifier circuit in grounded coplanar waveguide topology demonstrating a linear gain of 13 dB at 450 GHz. Assuming matching losses of 1.5 dB per stage within the MMIC the measured circuit gain of 3.3 dB per stage is in good agreement with the 4.6 dB transistor gain predicted by the small signal model.