Search

The monolithic integration of enhancement/depletion-mode (E/D-mode) HEMTs in the GaN material system is demonstrated based on a novel technique of fabricating high-performance E-mode HEMT using fluoride-based C[F.sub.4] plasma treatment. The integration technology, used to fabricate integrated AlGaN/GaN HEMT inverters and ring oscillators for evaluating the performance of the digital IC technology, results in an improved input voltage swing by about 1V for the E-mode HEMT.

Fabrication and characterization of AlGaN/GaN HEMT inverters and ring oscillators utilizing integrated enhancement/depletion-mode (E/D-mode) AlGaN/GaN HEMTs are presented. The core technique is a CF4 plasma treatment that can effectively convert a D-mode AlGaN/GaN heterostructure to an E-mode heterostructure. A significant advantage of the plasma-treated E-mode HEMTs is that the gate current is reduced in both reverse- and forward-bias regions due to the effectively enhanced barrier height induced by the negatively charged fluorine ions in the AlGaN barrier. As a result, the input voltage swing is expanded by about 1 V for the E-mode HEMT, enabling convenient input/output logic level matching for multistage logic circuits such as ring oscillators. The fabricated 17-stage direct-coupled field-effect transistor logic ring oscillator using the 1-μm-gate technology can operate properly at a larger supply voltage of 3.5 V, and a minimum propagation delay of 130 ps/stage is achieved. [ABSTRACT FROM AUTHOR]