| This dissertation is part of an on-going effort at the State University of New York at Stony Brook in search of a practical Josephson array oscillator as a high-power, submillimeter wave-length source using a distributed series array of Nb/AlOx/Nb Josephson junctions. The target frequency is 1 THz, the target output power 1 mW, the target linewidth parts in 10-6. Such oscillators are highly desirable for technical applications, especially for satellite installations, due to the non-availability of other compact, tunable, power-efficient, and reliably electronically controllable radiation sources in this frequency range. This dissertation describes the use of self-shunted, high critical current density Nb/AOx/Nb junctions for array oscillator applications. Since the product of critical current (Ic) and normal resistance (R n) of such junctions is approximately 2 mV, they are ideally suitable for operation at approximately 1 THz. There are many other important technical issues to be solved for the successful operation of a high critical current density Josephson array oscillator, among which the most important are the limitation of RF losses inside the transmission line interconnecting the junctions of the array, the uniformity of the junction parameters Ic and Rn, and the dissipation of the heat generated by DC biasing the junctions. There are trade-offs, e.g. larger junction dimensions might ensure better uniformity, but make self-heating more severe. Phase-locking experiments between high critical current density junctions of different shape and size were performed, in order to test how much junction non-uniformity can be tolerated in a series-biased array oscillator, and heating experiments were performed to determine how much power dissipation in the junctions can be handled. The experiments conducted show the feasibility to fabricate distributed series arrays of approximately 1000 self-shunted high critical current Josephson junctions which will be capable of delivering 2.5 mW of RF power at 1 THz to a 50 W load. Some related topics, which are also discussed in this dissertation, are the quasi-optical coupling of millimeter wave radiation from a Josephson array source with an on-chip logarithmic spiral antenna to free space, the power measurement of this radiation with a Si composite bolometer, and the linewidth measurement with an SIS mixer. |
