Superconducting quantum detectors

Abstract:

The Cold-Electron Bolometer (CEB) is a sensitive millimetre-wave detector which is easy to integrate with superconducting planar circuits. CEB detectors have other important features such as high saturation power and very fast response. We have fabricated and tested CEB detectors integrated across the slot of a unilateral finline on a silicon substrate. Bolometers were fabricated using two fabrication methods: e-beam direct-write trilayer technology and an advanced shadow mask evaporation technique. The CEB performance was tested in a He3 sorption cryostat at a bath temperature of 280mK. DC I-V curves and temperature responses were measured in a current bias mode, and preliminary measurements of the optical response were made using an IMPATT diode operating at 110GHz. These tests were conducted by coupling power directly into the finline chip, without the use of waveguide or feedhorns. For the devices fabricated in standard direct-write technology, the bolometer dark electrical noise equivalent power is estimated to be about 5×10-16W/ √Hz, while the dark NEP value for the shadow mask evaporation technique devices is estimated to be as low as 3×10-17W/√Hz. © 2010 SPIE.

Abstract:

We present the design of two niobium singleended Superconductor-Insulator-Superconductor (SIS) mixers optimized to work in the frequency range of 600–700 GHz. A key feature of this new mixer design is the utilization of a unilateral finline taper. This transition is significantly easier to design and simulate than the previously employed antipodal finline, and more importantly it simplifies the chip fabrication considerably since the fins do not overlap at any stage. RF power propagating in the finline is coupled to the microstrip either directly from the slotline to microstrip, or more efficiently via a coplanar waveguide (CPW). Another novel feature of our design is the fabrication of the mixer chip on a very thin silicon substrate which will be achieved using Silicon-On-Insulator (SOI) technology. This will allow easy matching of the incoming signal from the feed horn to the loaded waveguide and allows the lightweight mixer chip to be held in the E-plane of the waveguide using gold beam leads, eliminating the need for a deep groove in the waveguide wall. These new features yield a significantly shorter chip and allow wider RF bandwidth since the excitation of higher order modes in the groove has been avoided. The mixer block is extremely simple, composing a smooth-walled horn and a waveguide section without any complicated mechanical features. In this paper, we present the details of the mixer chip, including various transition sections, tuning circuits and mixer block designs, supported by electromagnetic simulations. We describe the design procedure in detail and predict the full mixer performance using the SuperMix software package.