Heterojunction GaAs/GaAlAs I2L-ring oscillators fabricated by MBE

GaAs/GaAlAs heterojunction bipolar transistors have been made and integrated to a seven-stage I²L-ring oscillator. The five layer sequence has been grown by MBE. The transistor operating upside down (inverted, collector on the top) exhibits a current gain up to 50 for one collector. A groove isolation technique has been used to isolate the gates from each other. The structure was planarized by polyimide, incorporated Ta thin-film resistors for the injectors as well as implanted resistors. A delay time of 3.0 ns at 60-µW power consumption has been achieved in the low power region which corresponds to a power delay product of 0,18 pJ and a minimum delay time of 700 ps has been obtained at 1 mW.