Thirty-five-nm T-Gate In0.52Al0.48As/In0.53Ga0.47As metamorphic HEMTs with an ultrahigh fmax of 610 GHz

Thirty-five-nanometer T-gate GaAs-based In0.52Al0.48As/In0.53Ga0.47As metamorphic high electron mobility transistors (mHEMTs) are successfully fabricated using a zigzag-shaped T-gate. We obtain a maximum extrinsic transconductance (gm) of 1060 mS/mm and a maximum oscillation frequency (fmax) of 610 GHz. These superior results are obtained by reducing the T-gate's length to 35 nm without the assistance of a supporting layer and by fabricating a wide-recessed-gate structure. The stand-alone 35-nm T-gate effectively improves the device performance because it doesn't cause additional parasitic capacitances. The wide-recessed-gate structure alleviates impact ionization in the channel, which suppresses the kink effect in the output characteristic and reduces the output conductance (gds). In addition, the wide-recessed-gate structure reduces the gate-to-drain capacitance (Cgd); consequently realizing a state-of-the-art fmax. The fmax of 610 GHz, to our knowledge, is the highest value reported to date for GaAs-based HEMTs.