Monolithic integration of enhancement-and depletion-mode AlGaN/GaN HEMTs for GaN digital integrated circuits

We demonstrate a novel technique for monolithic integration of enhancement and depletion-mode AlGaN/GaN HEMTs using CF₄ plasma treatment. Direct-coupled FET logic circuits such as an E/D HEMT inverter and a 17-stage ring oscillator are demonstrated in GaN system for the first time. At a supply voltage (V_DD)of 1.5V, the fabricated E/D inverter shows an output logic swing of 1.25V, logic-low noise margin of 0.21V and logic-high noise margin of 0.51V. The fabricated ring oscillator shows a minimum delay of 130 ps/stage at V _DD = 3.5 V, and a minimum power-delay product of 0.113 pJ/stage at V_DD = 1 V