Aaron M. Datesman

Fabrication and characterization of niobium diffusion-cooled hot-electron bolometers on silicon nitride membranes

We have successfully fabricated niobium diffusion-cooled hot-electron bolometer (HEB) mixers on membranes of silicon nitride less than one micron thick. This advance has allowed us to construct a 1 /spl times/ 5 HEB receiver array intended for operation at 1.45 THz. This article provides an overview of the integration of the HEB array chip with silicon micromachined backshorts and feedhorns, discusses materials issues surrounding the device fabrication, reports resistance and I-V measurements, and compares HEBs fabricated on silicon nitride to similar devices on quartz substrates.

A new fabrication technique for ultra-small diffusion-cooled hot-electron bolometers

Hot-electron bolometers (HEBs) are becoming the technology of choice for heterodyne mixing in the short submillimeter wavelength regime (frequencies above 1 THz). In this paper, we describe a new, versatile, easily variable method of diffusion-cooled HEB fabrication using a focused-ion beam (FIB) microscope. This technique does not require electron-beam lithography or definition of the bolometer element by lift-off.

Gallium ion implantation into niobium thin films using a focused-ion beam

We have implanted 30 keV gallium ions into niobium films 100 /spl Aring/ thick using a focused-ion beam (FIB). The nature of the FIB tool allows the irradiation of a specific, controllable, area of the substrate, from hundreds of square microns down to an arbitrary, user-defined pattern defined by a 70 /spl Aring/ stencil. A sacrificial layer of gold covering the niobium controls the range of the incident gallium ions and prevents the niobium film from sputtering away under bombardment. This article examines the behavior of these films phenomenologically, including information about the changes in transition temperature and resistance of the implanted samples. Also a curious unexplained feature of the resistive transition at implant doses below about 3/spl times/10/sup 19/ cm/sup -3/ will be presented and discussed.

Fabrication of a superconducting hot-electron bolometer receiver with micromachined waveguide components

The use of superconducting hot-electron bolometers (HEBs) as mixing elements in terahertz heterodyne receivers has become increasingly attractive in the last few years. Such receivers find application in the fields of radio astronomy, molecular spectroscopy, and atmospheric remote sensing. We have developed a method of fabricating these devices, consisting of a niobium film less than one-quarter micron long and 150 /spl Aring/ thick, using a gallium focused-ion beam (FIB). We intend to build a mixer which incorporates these devices, fabricated on silicon nitride membranes, with terahertz waveguide components fabricated by laser-micromachining of silicon under CAD control. This paper discusses the three fabrication methods (focused-ion beam, the bulk micromachining of silicon necessary to obtain nitride membranes, and laser micromachining) used in our work.

Electron-Beam Deposition of Superconducting Molybdenum Thin Films for the Development of Mo/Au TES X-ray Microcalorimeter

We are exploring the properties of electron-beam evaporated molybdenum thin films on silicon nitride coated silicon wafers at substrate temperatures between room temperature and 650°C. The temperature dependence of film stress, transition temperature, and electrical properties are presented. X-ray diffraction measurements are performed to gain information on molybdenum crystallite size and growth. Results show the dominant influence of the crystallite size on the intrinsic properties of our films. Wafer-scale uniformity, wafer yield, and optimal thermal bias regime for TES fabrication are discussed.

A Simple GHz Resonator for Superconducting Materials Characterization

This work examines the design and operation of a longitudinal resonant cavity, paired with monopole send and reciprocal patch receive antennae, that couples radio-frequency energy to a superconducting thin film carrying high current densities (~105 A/cm2). The dielectric substrate supporting the film penetrates the waveguide, which operates in an evanescent mode below the design cutoff frequency of 18 GHz. Oscillatory vortex motion in the thin film is found to produce a small (~0.1 mV) dc voltage. When the niobium film is patterned to form an aperture that permits resonant conditions within the waveguide volume, the measured voltage increases by an order of magnitude. The increase is explained in the framework of the Larkin-Ovchinnikov model for quasiparticle behavior inside a moving normal vortex core. Operated near the superconducting transition, this device is useful for materials characterization, including the possibility to extract parameters including the pinning force. The authors suggest that the device could be used to characterize the pinning potential or to explore quasiparticle dynamics in superconducting thin films.