Monolithic integrated enhancement/depletion-mode AlGaN/GaN high electron mobility transistors with cap layer engineering

Monolithic integrated enhancement/depletion (E/D)-mode AlGaN/GaN high electron mobility transistors (HEMTs) are fabricated on an AlGaN/GaN heterostructure with an engineered triple-cap-layer. The energy band of the cap layer is greatly tailored by the polarizations within it, which improves the controllability of D-to-E mode conversion with gate recess. The uniformity of the threshold voltage (Vth) across a 3″ wafer is assessed and the standard deviations of Vth are 0.1 V and 0.14 V for E-mode and D-mode devices, respectively. Direct-coupled field-effect transistor logic E/D HEMT inverter and 17-stage ring oscillator are demonstrated, and the latter shows a oscillation frequency of 201 MHz at a supply voltage of 1 V, corresponding to a propagation delay of 146 ps/stage and a power-delay product of 1.96 pJ/stage.