Interest in THz technology is growing, with projects such as the Atacama large millimeter array (ALMA) astronomical observatory, biohazard remote detection, high frequency radar and other detection systems. This paper presents the design, fabrication and test results of a 1.6 THz superconducting phonon-cooled NbN hot electron bolometer. Elements of the mixer design, including simulation results and S-parameters, are presented. A novel fabrication process, the suspended sidewall nano patterned stencil (SSNaPS) procedure, along with unique thin silicon backside processing, is used to create these THz mixers. For the phonon-cooled mixer, a receiver noise temperature of 3474 K and a mixer noise temperature of 613 K were obtained. DC characterization and RF test results are discussed.

Six-port reflectometers have become a topic of interest due to the scarcity of instrumentation for measuring scattering parameters (s-parameters) at terahertz frequencies. This paper presents a quasi-optical six-port reflectometer designed for 585 GHz using hot-electron bolometers (HEB's). In this design, a ring slot antenna couples a signal into the reflectometer creating a standing wave along a microstrip transmission line. The standing wave is sampled by three evenly spaced HEB's. A polarization rotation resulting from the feed of the transmission line allows the antenna to act as both the input and measurement ports (horizontally polarized energy is coupled into the device and re-radiated with vertical polarization). The reflectometer is expected to be sensitive to nanowatt power levels from 570 GHz to 640 GHz. The annular slot antenna and microstrip portion of the device have been independently fabricated and tested. This proof-of-concept test verifies that the polarization is rotated and provides an estimate of the power available for sampling. It was found that approximately 30 μW of power is available, as measured with an Erickson power meter. Simulations in conjunction with these data indicate that the HEB's should be capable of detecting 100's of nanowatts. This requires each HEB to have approximate dimensions of 100nm by 200nm. This paper presents the six-port design and preliminary measurements. I. INTRODUCTION A six-port reflectometer is a compact and relatively inexpensive method for measuring scattering parameters that has outstanding potential for characterizing terahertz components and materials. The realization of such a device at terahertz frequencies would permit diagnostic and measurement capabilities not currently available. Potential uses include characterizing materials such as absorbers, windows, lenses, and other components used in terahertz systems. The six-port reflectometer presented in this work will be realized using three diffusion cooled niobium hot- electron bolometers operating as direct detectors. The input and measurement ports will utilize the antenna using a rotation in the polarization of the signal.

While the superconducting community has developed various techniques for the fabrication of nanoscale hot electron bolometers (HEB), the basic structure of an HEB microbridge has been fairly consistent. A typical HEB used in a cryogenic terahertz mixer consists of a thin strip of superconductor contacted on opposite ends by small metal contact pads in a planar configuration. Both the physics and typical fabrication requirements for HEBs inspire this traditional construction. In this paper, however, we demonstrate that alternative HEB geometries are possible, which can in some cases improve the ease of fabrication, alter device characteristics, or alleviate certain device limitations. New HEB structures and associated fabrication processes are presented, building on previous work using the SSNaPS method of nanoscale patterning. These include very short niobium nitride HEBs with self-aligned bridge etch masks, and sidewall-patterned niobium HEB microbridges.

We report on receiver noise measurement results of phonon-cooled HEB beam lead mixers on 3 /spl mu/m thick silicon. This type of ultra-thin mixer chip with integrated beam leads allows easy assembly into a block and holds great promise for array integration. Receiver measurements from 600-720 GHz are presented with a minimum noise temperature of 500 K at 666 GHz. These results verify the mixer performance of the SOI processing techniques allowing for further design and integration of SOI pHEB mixers in receivers operating above 1 THz.

Superconducting based SIS and HEB detectors continue to yield improved noise temperatures at submillimeter wavelengths. These higher frequencies present new challenges, particularly for waveguide based designs where the tolerances for mounting small mixer chips become quite narrow. Also, conventional millimeter wavelength techniques for making the IF and ground connections are more prone to error. As the device technology for these SIS and HEB-based detectors matures, there is also an increased interest in integrated receiver arrays. These challenges call for simpler mounting designs and more repeatable assembly techniques. Our research group, at the University of Virginia, is meeting these challenges with a new ultra-thin mixer chip technology, with integrated gold beam leads, first reported in [1]. We have since further developed and improved on this technology. We have several ongoing SIS, HEB and OMT projects which utilize these capabilities. Most important to this technology is the transition from the conventional use of quartz as a circuit substrate material to that of ultra-thin (<10 microns) silicon. We accomplish this by creating the mixer circuitry on a silicon-on-insulator (SOI) wafer and using a sophisticated backside release process to produce individual mixer chips. These 3 micron ultra-thin chips present less dielectric material within a waveguide channel and are actually much more robust than quartz chips that are an order of magnitude, or more, thicker. We use integrated 1-2 micron thick gold beam leads to simplify the electrical connection and placement of the chip within the receiver waveguide. Beam leads are another component of the mounting process that makes our modular mixer implementation possible. Based on our SOI process, we are currently developing several HEB mixerstwo single element metal waveguide designs at 600 GHz and 1.6 THz, and an integrated array approach using silicon laser micromachined blocks centered at 900 GHz and 1.8 THz. We are also pursuing several SIS mixersone single element 350-500 GHz design with ultra wide IF bandwidth and one 350 GHz receiver array. In this paper we will discuss our ultra thin silicon beam lead technology and the ongoing progress of these new receivers.

The assembly of superconducting millimeter and submillimeter-wave circuits becomes increasingly difficult as chip dimensions and design tolerances shrink with increased operating frequency. Currently, RF ground connections are made by soldering, wire bonding or with conductive wire gaskets. To facilitate assembly and throughput, we are developing a beam lead process for quartz chips. Such processes already exist for silicon and gallium arsenide wafers. However, niobium circuits on quartz substrates present unique difficulties. SIS junctions introduce additional thermal and chemical constraints to process development. For quartz, wet etches are isotropic and dry etches with high etch rates require large ion energies. We have developed a new, top-side approach to beam lead fabrication suitable for whole wafer processing.

The platelet immuno-assay (PIA) is a simple and inexpensive technique to detect antigens with ng/ml sensitivity using micro-titer equipment and commercially available antisera. It can be easily adapted for virtually any antigen to which rabbit antiserum containing specific IgG-antibodies cna be obtained. The assay is inhibited by IgG and C1q in amounts greater than or equal to 125 microgram/ml and 12.5 microgram/ml respectively. Its application is thus limited to those fluids where IgG and C1q are present in less than these concentrations.

Most writing on Australian policy-making towards the Pacific states describes its operation in terms of relatively simple processes. The most prominent among these are responses to changes in the security environment, shifting ideas that inform understandings of Australia's relationship with its region, and liberal or Marxist conceptions of material interests. In each case the driving factor is exogenous to the policy-making process. This paper proposes that applying the tools of institutionalism to the Australian policy-making processes will yield a more fruitful analysis. Institutionalism is characterised by its consideration of a relatively wide range of independent variables, broken down into three categories: ideas, interests and institutions. By considering the regional security environment as an institutional arrangement alongside the material interests and ideas of the regional relationship as three dimensions of the policy process it affords the possibility of incorporating into a single analysis the insights of the three prominent schools. In so doing it can yield greater explanatory power than the sum of its parts by creating a framework within which the inter-relations of the institutions, ideas and interests may be explored. A wider range of independent variables leads to analyses that are more complex, drawing attention to the path-dependency of historical processes and unintended consequences of decisions, the asymmetries of power associated with political institutions and the tendency towards continuity in the face of change. This paper argues that these features of institutionalism can incorporate some of the particularities that tend to be overlooked in analyses of Australian policy making toward the Pacific states. Most notable among these are the great asymmetries of power in the relationships and the tendency towards bipartisanship and continuity.

We present a process for fabricating ultra-thin silicon chips for submillimeter-wave mixing applications using SOI (Silicon On Insulator) wafers. Such chips allow the profile of the mixer substrate to be minimized within the microstrip channel, thereby simplifying RF design considerations and minimizing machining constraints. The chips feature gold beam leads, RF filter structures, and hot-electron bolometers as the non-linear element.