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The sensitivity of a bolometer is in principle limited by the phonon noise, which is a function of the conductance between its absorber and the thermal sink. However, practical issues limit the degree to which conductance can be minimized. For example, in a high-radiation environment, extremely low conductance, or, equivalently, long thermal recovery time, can lead to high data loss. To circumvent such limitations, we are developing a technique of modulating the conductance through the use of pixel-scale superconducting heat switches. We have fabricated bolometer-like test devices consisting of isolated regions connected to a thermal ground plane through narrow aluminum strips. Niobium coils are patterned around the aluminum strips. Flowing current through a coil allows the aluminum to be driven into the normal or high thermal conductance state. We have measured the conductance of these devices as a function of temperature and drive coil current. [ABSTRACT FROM AUTHOR]

Future ground and space-based astronomy missions in the millimeter and sub-millimeter range will rely upon kilopixel detector arrays. We are developing a superconducting Transition-Edge Hot-Electron Bolometer (THM) for use in these next generation missions. Thermal isolation of the THM is controlled by the hot-electron effect between the electrons and phonons within the small volume of the superconducting detector. To reach noise levels near the photon background noise for observing the Cosmic Microwave Background (CMB) and the submillimeter and far-infrared background the optimal detector size occurs at the micron length scale. We present measurements of the thermal conductance of two micron-sized THM devices which show a hot-electron temperature dependence and predict NEP\leq 5\times 10^-18\ W/\sqrtHz for CMB loading conditions and NEP\leq 1\times 10^-19\ W\sqrtHz in the low power loading limit. We also briefly discuss the detector geometry and thermal conductance optimization for CMB loading conditions. [ABSTRACT FROM AUTHOR]

We describe measurements of the properties, at dc, gigahertz, and terahertz frequencies, of thin (10 nm) aluminum films with 10 Ω/square normal state sheet resistance. Such films can be applied to construct microwave kinetic inductance detector arrays for submillimeter and far-infrared astronomical applications in which incident power excites quasiparticles directly in a superconducting resonator that is configured to present a matched-impedance to the high frequency radiation being detected. For films 10 nm thick, we report normal state sheet resistance, resistance-temperature curves for the superconducting transition, quality factor and kinetic inductance fraction for microwave resonators made from patterned films, and terahertz measurements of sheet impedance measured with a Fourier Transform Spectrometer. We compare properties with similar resonators made from niobium 600 nm thick. [ABSTRACT FROM AUTHOR]

Membrane-structured superconducting MgB2 thin films are potential candidates for the development of moderately cooled bolometers sensitive to far infrared radiation. On the path to developing such devices, we present a comparison of three etching techniques for MgB2 thin films namely, chlorine plasma etch, aqueous hydrochloric acid etch and an aqueous nitric acid etch. Out of the three etch techniques, the aqueous 50% nitric acid solution etch, using standard photolithography, proved to have a high MgB2 etch rate (>51 nm/s), with better sidewall delineation and selectivity to the underlying SiN-film-coated Si substrate, moreover the etched film structure showed good superconductivity transition characteristics, namely, a superconducting critical transition at 38.57 ± 0.6 K, a transition width of 0.09 K and a RRR of 2.22. [ABSTRACT FROM AUTHOR]

We are developing a Transition-edge Hot-electron Microbolometer (THM) with the capacity to make sensitive and broadband astrophysical observations over frequencies ranging from 30-300 GHz (10-1 mm). This micron-sized bolometer consists of a superconducting bilayer Transition-Edge Sensor (TES) and a thin-film absorber. The THM employs the decoupling between electrons and phonons at low temperatures (below 300 mK) to provide thermal isolation. The devices are fabricated photolithographically and read out with Superconducting Quantum Interference Devices (SQUIDs). We present the details of a thermal model for a THM detector and the design for new thermally optimized antenna-coupled THMs for illumination by a RF source at 40 and 100 GHz. [ABSTRACT FROM AUTHOR]

This paper describes the fabrication of small aluminum tunnel junctions for applications in astronomy. Antenna-coupled superconducting tunnel junctions with integrated single-electron transistor readout have the potential for photon-counting sensitivity at sub-mm wavelengths. The junctions for the detector and single-electron transistor can be made with electron-beam lithography and a standard self-aligned double-angle deposition process. However, high yield and uniformity of the junctions is required for large-format detector arrays. This paper describes how measurement and modification of the sensitivity ratio in the resist bilayer was used to greatly improve the reliability of forming devices with uniform, sub-micron size, low-leakage junctions. [ABSTRACT FROM AUTHOR]

Describes radio-frequency single-electron transistors with large input gates for use as on-chip amplifiers for high impedance cryogenic photodetectors. Modes of operation; Amplifier feedback configurations; Amplifier outputs; Input gate capacitance.

We present the first measurement results for silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) and SiGe BCMOS circuits operating in the sub-1-K regime. Robust transistor operation of a first-generation 0.5 x 2.5 x 4-μm² SiGe transistor is demonstrated at package temperatures as low as 300 mK. In addition, a SiGe BiCMOS bandgap voltage reference is verified to be fully functional at operating temperatures below 700 mK. The SiGe voltage reference exhibits a temperature coefficient of 160 ppm/°C over the temperature range of 700 mK-300 K. [ABSTRACT FROM AUTHOR]