Depletion- and enhancement-mode modulation-doped field-effect transistors for ultrahigh-speed applications: An electrochemical fabrication technology

This paper is devoted to an electrochemical-etching-based technology for fa bricating high-performance MODFET's for high-speed applications. The electr ochemical etching in the gate openings is induced by the exposure of the Ki surface metal on the ohmic electrodes, It results in very slender gate-rec ess grooves, which are desirable for high-speed MODFET's because of the res ulting achievable small gate-to-channel separation and low parasitic resist ance. The technology is easy to implement, and is effective for enhancing t he aspect ratio, Good control of aspect ratio is essential for achieving ex cellent device performance and limiting deleterious short-channel effects, Successful vertical:scaling, together with minimization of gate length by w ell-established electron-beam lithography using fullerene-incorporated elec tron-beam resist, leads to the realization of both optimal D- and E-mode MO DFET's with ultrahigh extrinsic transconductance values and current gain cu t-off frequencies. Fully passivated 0.07-mu m D-MODFET's with 2.25 S/mm ext rinsic transconductance and current gain cut-off frequency exceeding 300 GH z have been successful fabricated. In addition, 0.03-mu m E-MODFET's with 2 S/mm transconductance and 300 GHz current gain cut-off frequency have been demonstrated. This electrochemical-etching-based technology provides both high-performance D- and E-MODFET's and, therefore, opens up the possibility to achieve ultrahigh-speed IC's based on DCFL configurations.