High-speed low-voltage ring oscillators based on selectively doped heterojunction transistors

We report ring oscillators which attain high speed at low supply voltage, and thus low power. Selectively doped heterojunction transistors (SDHT's) were used in a direct-coupled circuit. The GaAs/ Al.3Ga.7As heterostructure, grown by MBE, was designed to allow self-limiting etch of the gate recesses in the driver transistors. Devices with 1 µm gates operated at supply voltages as low as 0.23 V at T = 300 K. At 77 K, gate delays as low as 14.7 ps were observed at 1.0-V bias.