119 research outputs found
Cryogenic probe station for on-wafer characterization of electrical devices
A probe station, suitable for the electrical characterization of integrated circuits at cryogenic temperatures is presented. The unique design incorporates all moving components inside the cryostat at room temperature, greatly simplifying the design and allowing automated step and repeat testing. The system can characterize wafers up to 100 mm in diameter, at temperatures <20 K. It is capable of highly repeatable measurements at millimeter-wave frequencies, even though it utilizes a Gifford McMahon cryocooler which typically imposes limits due to vibration. Its capabilities are illustrated by noise temperature and S-parameter measurements on low noise amplifiers for radio astronomy, operating at 75–116 GHz
Coherent polarimeter modules for the QUIET experiment
The Q/U Imaging Experiment (QUIET) is an experimental program to make very sensitive measurements of the Cosmic Background Radiation (CMB) polarization from the ground. A key component of this project is the ability to produce large numbers of detectors in order to achieve the required sensitivity. Using a breakthrough in mm-wave packaging at JPL, a polarimeter-on-a-chip has been developed which lends itself to the mass-production techniques used in the semiconductor industry. We describe the design, implementation and performance of these polarimeter modules for QUIET Phase I and briefly discuss the plans for further module development
Coherent Arrays for Astronomy and Remote Sensing - Final Report
The Coherent Arrays for Astronomy and Remote Sensing Program sponsored by the
Keck Institute for Space Studies has had a profound impact on astronomy at Caltech –
both at JPL and on campus – and worldwide. It provided funds for the establishment of a
world-class coherent detector laboratory – the Cahill Radio Astronomy Laboratory
(CRAL) that, in collaboration with JPL and Northrop Grumman, now sets the global
standard in coherent detectors in the centimeter-millimeter wavelength range – as shown
by three key highlights: (i) NRAO’s recent selection of CRAL MMIC detectors over its
own in house MIC detectors for the upgrade of the ALMA Band 2 receivers; (ii) NSF’s
funding of a 16-element 85 GHz – 115 GHz focal plane array (ARGUS) for the Green
Bank Telescope (2.5M). The funding of COMAP was particularly important
since it demonstrated in the wake of the NSF decline of the CARMA proposal (2014) that
the US astronomy community and the NSF were prepared to fund large new projects at
the Owens Valley Radio Observatory (OVRO), enabling the OVRO to re-establish itself
as a world-class radio observatory and convincing Caltech to continue its funding of the
OVRO. It is no exaggeration that the KISS coherent detector program played THE major
role in saving the OVRO. The position of the CRAL and of the OVRO is now very
strong and the staff, decimated by the CARMA decline, is being rebuilt and is once more
at a robust strength. Two new multi-national partnerships – the Radio Astronomy
Partnership (RAP) and the MMIC Partnership (MMICP) have been established at Caltech
as a direct result of the KISS investment in creating the CRAL, and these are providing
independent funding to OVRO and the CRAL. There are now eight agency-funded
programs at the OVRO and we are optimistic about the prospects of having two more
programs funded in the next year, in view of important science breakthroughs at OVRO
over the last 6 months
The STRIP instrument of the Large Scale Polarization Explorer: microwave eyes to map the Galactic polarized foregrounds
In this paper we discuss the latest developments of the STRIP instrument of the “Large Scale Polarization Explorer” (LSPE) experiment. LSPE is a novel project that combines ground-based (STRIP) and balloon-borne (SWIPE) polarization measurements of the microwave sky on large angular scales to attempt a detection of the “B-modes” of the Cosmic Microwave Background polarization. STRIP will observe approximately 25% of the Northern sky from the “Observatorio del Teide” in Tenerife, using an array of forty-nine coherent polarimeters at 43 GHz, coupled to a 1.5 m fully rotating crossed-Dragone telescope. A second frequency channel with six-elements at 95 GHz will be exploited as an atmospheric monitor. At present, most of the hardware of the STRIP instrument has been developed and tested at sub-system level. System-level characterization, starting in July 2018, will lead STRIP to be shipped and installed at the observation site within the end of the year. The on-site verification and calibration of the whole instrument will prepare STRIP for a 2-years campaign for the observation of the CMB polarization
125 - 211 GHz low noise MMIC amplifier design for radio astronomy
To achieve the low noise and wide bandwidth required for millimeter wavelength astronomy applications, superconductor-insulator-superconductor (SIS) mixer based receiver systems have typically been used. This paper investigates the performance of high electron mobility transistor (HEMT) based low noise amplifiers (LNAs) as an alternative approach for systems operating in the 125 — 211 GHz frequency range. A four-stage, common-source, unconditionally stable monolithic microwave integrated circuit (MMIC) design is presented using the state-of-the-art 35 nm indium phosphide HEMT process from Northrop Grumman Corporation. The simulated MMIC achieves noise temperature (T_e) lower than 58 K across the operational bandwidth, with average T_e of 38.8 K (corresponding to less than 5 times the quantum limit (hf/k) at 170 GHz) and forward transmission of 20.5 ± 0.85 dB. Input and output reflection coefficients are better than -6 and -12 dB, respectively, across the desired bandwidth. To the authors knowledge, no LNA currently operates across the entirety of this frequency range. Successful fabrication and implementation of this LNA would challenge the dominance SIS mixers have on sub-THz receivers
A Physical Model for Drain Noise in High Electron Mobility Transistors: Theory and Experiment
We report the on-wafer characterization of -parameters and microwave noise
temperature () of discrete metamorphic GaAs high electron mobility
transistors (HEMTs) at 40 K and 300 K over a range of drain-source voltages
(). From these data, we extract a small-signal model and the drain
noise temperature () at each bias and temperature. We find that
follows a superlinear trend with at both temperatures. These trends
are interpreted by attributing drain noise to a thermal component associated
with the channel resistance and a component due to real-space transfer (RST) of
electrons from the channel to the barrier [1]. In the present devices at the
minimum , RST contributes % of the drain noise at cryogenic
temperatures. At 300 K, the contribution increases to over % of the
total drain noise. This finding indicates that improving the confinement of
electrons in the quantum well could enable room-temperature receivers with up
to % lower noise temperatures by decreasing the contribution of RST to
drain noise.Comment: 6 pages, 6 figure
Centimeter-wave continuum radiation from the rho Ophiuchi molecular cloud
The rho Oph molecular cloud is undergoing intermediate-mass star formation.
UV radiation from its hottest young stars heats and dissociates exposed layers,
but does not ionize hydrogen. Only faint radiation from the Rayleigh-Jeans tail
of ~10-100K dust is expected at wavelengths longwards of 3mm. Yet Cosmic
Background Imager (CBI) observations reveal that the rho Oph W
photo-dissociation region (PDR) is surprisingly bright at centimetre
wavelengths. We searched for interpretations consistent with the WMAP radio
spectrum, new ISO-LWS parallel mode images and archival Spitzer data.
Dust-related emission mechanisms at 1 cm, as proposed by Draine & Lazarian, are
a possibility. But a magnetic enhancement of the grain opacity at 1cm is
inconsistent with the morphology of the dust column maps Nd and the lack of
detected polarization. Spinning dust, or electric-dipole radiation from
spinning very small grains (VSGs), comfortably explains the radio spectrum,
although not the conspicuous absence from the CBI data of the infrared
circumstellar nebulae around the B-type stars S1 and SR~3. Allowing for VSG
depletion can marginally reconcile spinning dust with the data. As an
alternative interpretation we consider the continuum from residual charges in
rho Oph W, where most of carbon should be photoionised by the close binary
HD147889 (B2IV, B3IV). Electron densities of ~100 cm^{-3}, or H-nucleus
densities n_H > 1E6 cm^{-3}, are required to interpret rho Oph W as the CII
Stromgren sphere of HD147889. However the observed steep and positive
low-frequency spectral index would then require optically thick emission from
an hitherto unobserved ensemble of dense clumps or sheets with a filling factor
~1E-4 and n_H ~ 1E7 cm^{-3}.Comment: accepted for publication in MNRA
Investigation of Cryogenic Current-Voltage Anomalies in SiGe HBTs: Role of Base-Emitter Junction Inhomogeneities
The anomalous current-voltage characteristics of cryogenic SiGe
heterojunction bipolar transistors (HBTs) have been a topic of investigation
for many years. Proposed explanations include quasiballistic transport of
electrons across the base or tunneling from the emitter to the collector, but
inconsistencies exist with these hypotheses. Although similar behavior occurs
in Schottky junctions and has been attributed to spatial inhomogeneities in the
base-emitter junction potential, this explanation has not been considered for
SiGe HBTs. Here, we experimentally investigate this hypothesis by
characterizing the base-emitter junction ideality factor and built-in potential
of a SiGe HBT versus temperature using a cryogenic probe station. The
temperature-dependence of the ideality factor and the relation between the
built-in potential as measured by capacitance-voltage and current-voltage
characteristics are in good qualitative agreement with the predictions of a
theory of electrical transport across a junction with a Gaussian distribution
of potential barrier heights. These observations support the origin of
cryogenic electrical anomalies in SiGe HBTs as arising from lateral
inhomogeneities in the base-emitter junction potential. This work helps to
identify the physical mechanisms limiting the cryogenic microwave noise
performance of SiGe HBTs
- …