Modeling and Characterization of Bloch Oscillating Junction Transistors

Abstract

We have investigated quantum dynamics in small Josephson junction devices where Cooper pair and quasiparticle tunneling can be combined in an intricate way to provide amplification of current. These devices, called Bloch oscillating junction transistors (BOT), employ quasiparticle tunneling to trigger the transistor from a Bloch oscillating state in the coherent limit to a Coulomb blockaded state. We describe the theory of BOTs in terms of the phase fluctuation theory and the energy band structure, which arises from the delocalization of the phase variable. Experimentally measured device characteristics are compared with theory and extensive simulations. The current gain of our devices obtained in a stable (non-hysteretic) operating mode amounts to as high as 30. Measurements on input impedance, noise temperature, and power gain show that the BOT operates best as an amplifier in the mid-range impedances, extending from 100 kΩ−−10 MΩ.