Art Lichtenberger

Terahertz micromachined on-wafer probes: Repeatability and robustness

Although progress has been made in the development of submillimeter-wave monolithic integrated circuits, the evaluation of these circuits still relies on test fixtures, which makes testing expensive and time consuming. Based on a W-band prototype, a micromachined on-wafer probe covering frequencies 500–750 GHz is built to simplify submillimeter-wave integrated circuits testing. This paper demonstrates the repeatability and the robustness of this terahertz micromachined on-wafer probe.

Performance of the pre-production band 3 (84-116 GHz) receivers for ALMA

The Band 3 receiver, covering the 84-116 GHz frequency band is one of the 10 channels that will be installed on the Atacama Large Millimeter Array (ALMA). A total of 73 units have to be built in two phases: 8 preproduction and then 65 production units. This paper reports on the assembly, testing and performance of the preproduction series of these state-of-the-art millimeter receivers.

Test and integration results from SuperCam: a 64-pixel array receiver for the 350 GHz atmospheric window

We report on both laboratory and telescope integration results from SuperCam, a 64 pixel imaging spectrometer designed for operation in the astrophysically important 870 micron atmospheric window. SuperCam will be used to answer fundamental questions about the physics and chemistry of molecular clouds in the Galaxy and their direct relation to star and planet formation. The SuperCam key project is a fully sampled Galactic plane survey covering over 500 square degrees of the Galaxy in 12CO(3-2) and 13CO(3-2) with 0.3 km/s velocity resolution In the past, all heterodyne focal plane arrays have been constructed using discrete mixers, arrayed in the focal plane. SuperCam reduces cryogenic and mechanical complexity by integrating multiple mixers and amplifiers into a single array module with a single set of DC and IF connectors. These modules are housed in a closed-cycle cryostat with a 1.5W capacity 4K cooler. The SuperCam instrument is currently undergoing laboratory testing with four of the eight mixer array modules installed in the cryostat (32 pixels). Work is now underway to perform the necessary modifications at the 10m Heinrich Hertz Telescope to accept the SuperCam system. SuperCam will be installed in the cassegrain cabin of the HHT, including the optical system, IF processing, spectrometers and control electronics. SuperCam will be integrated with the HHT during the 2009-2010 observing season with 32 pixels installed. The system will be upgraded to 64 pixels during the summer of 2010 after assembly of the four additional mixer modules is completed.

First observations with SuperCam and future plans

Supercam is a 345 GHz, 64-pixel heterodyne imaging array for the Heinrich Hertz Submillimeter Telescope (HHSMT). By integrating SIS mixer devices with Low Noise Ampliers (LNAs) in 8 - 1x8 pixel modules, the size needed for the cryostat and the complexity of internal wiring is signicantly reduced. All subsystems including the optics, cryostat, bias system, IF boxes, and spectrometer have been integrated for all 64 pixels. In the spring of 2012, SuperCam was installed on the HHSMT for an engineering run where it underwent system level tests and performed rst light observations. In the fall of 2012 SuperCam will begin a 500 square degree survey of the Galactic Plane in 12CO J=3-2. This large-scale survey will help answer fundamental questions about the formation, physical conditions, and energetics of molecular clouds within the Milky Way. The data set will be available via the web to all interested researchers.

Characterization of submillimeter-wave Schottky diodes in the 500–750 GHz band using micromachined on-wafer probes

For the first time, direct measurement and characterization of planar Schottky diodes using micromachined on-wafer probes operating from 500 to 750 GHz is described. The Schottky diodes are fabricated on a GaAs substrate and integrated into a coplanar waveguide to allow direct measurement of the device calibrated scattering parameters using CPW probes. The measurements are used to establish and verify equivalent circuit models and parasitics for submillimeter-wave diodes that, previously, were based solely on simulation or scaling of measurements done at microwave frequencies.

Micromachined probes for characterization of submillimeter-wave on-wafer components

Terahertz components and devices are typically interfaced with measurement instrumentation and characterized using fixtures equipped with waveguide flanges or antennas. Such fixtures are known to introduce significant uncertainty and error in measurements. It is preferable to characterize such devices in-situ, where the device under test can be measured on-wafer, prior to dicing and separately from the circuit housing to which it is ultimately affixed. This is commonly done in the RF and millimeter-wave region with a probe station equipped with coplanar launchers. Commercial coplanar waveguide probes have generally been available to the WR-2.2 band (325—500 GHz) but few options currently exist for on-wafer measurements above these frequencies. This paper describes recent work at the University of Virginia and Dominion Microprobes, Inc. to extend on-wafer measurement capabilities to terahertz frequencies through the design and implementation of coplanar probes based on silicon micromachining. At present micromachined on-wafer probes operating to WR1.2 (600 to 900 GHz) have been demonstrated and exhibit typical insertion losses lower than 7 dB with return loss of 15 dB or greater over a full waveguide band.

A 585 GHz annular-slot antenna coupled two-dimensional (two-D) focal-plane array utilizing twin-HEB devices

We report on the design and fabrication of 585 GHz focal-plane arrays utilizing annular-slot antennas and twin-HEB devices. Design details and simulation results are presented. DC characteristics of the twin-HEB devices, including R-T and I-V curves, have been tested. In addition, initial RF measurement results of the focal-plane array (FPA) mixers are presented.

Performance at 585 GHz of a slot-ring antenna coupled niobium HEB mixer element for imaging applications

585 GHz diffusion-cooled Nb HEB (d-HEB) mixers utilizing slot-ring antennas have been designed and fabricated on silicon wafers. To optimize power coupling from the antennas to the mixing elements, two impedance matching schemes are proposed. Performance at 585 GHz of the mixers including I-V curves, conversion gain and noise temperature are presented.