Hot-electron bolometer terahertz mixers for the Herschel Space Observatory

Department of Microtechnology and Nanoscience, Physical Electronics Laboratory, Chalmers University of Technology, SE-41296 Göteborg, Sweden.
Review of Scientific Instruments (Impact Factor: 1.58). 04/2008; 79(3):034501. DOI: 10.1063/1.2890099
Source: PubMed

ABSTRACT We report on low noise terahertz mixers (1.4-1.9 THz) developed for the heterodyne spectrometer onboard the Herschel Space Observatory. The mixers employ double slot antenna integrated superconducting hot-electron bolometers (HEBs) made of thin NbN films. The mixer performance was characterized in terms of detection sensitivity across the entire rf band by using a Fourier transform spectrometer (from 0.5 to 2.5 THz, with 30 GHz resolution) and also by measuring the mixer noise temperature at a limited number of discrete frequencies. The lowest mixer noise temperature recorded was 750 K [double sideband (DSB)] at 1.6 THz and 950 K DSB at 1.9 THz local oscillator (LO) frequencies. Averaged across the intermediate frequency band of 2.4-4.8 GHz, the mixer noise temperature was 1100 K DSB at 1.6 THz and 1450 K DSB at 1.9 THz LO frequencies. The HEB heterodyne receiver stability has been analyzed and compared to the HEB stability in the direct detection mode. The optimal local oscillator power was determined and found to be in a 200-500 nW range.

  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, 325 GHz antennas on chip mounted on a dielectric lens was investigated. The antennas on chip were analyzed with finite element method (FEM), including the S-parameters and impedance. The far-field radiation pattern of the lens integrated antenna is calculated synthesizing the FEM and geometrical optics (GO) based on ray launching. The extended hemispherical lens is optimized and a scaled model of the lens integrated log-periodic antenna is fabricated and measured. The measured results have good agreements with the simulation, implying the mentioned method.
    2012 International Conference on Microwave and Millimeter Wave Technology (ICMMT); 05/2012
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Terahertz high-resolution spectroscopy of interstellar molecular clouds greatly relies on hot-electron superconducting bolometric (HEB) mixers. Current state-of-the-art receivers use mixer devices made from ultrathin (~ 3-5 nm) films of NbN with critical temperature ~ 9-11 K. Such mixers have been deployed on a number of groundbased, suborbital, and orbital platforms including the HIFI instrument on the Hershel Space Observatory. Despite its good sensitivity and well-established fabrication process, the NbN HEB mixer suffers from the narrow intermediate frequency (IF) bandwidth ~ 2-3 GHz and is limited to operation at liquid Helium temperature. As the heterodyne receivers are now trending towards “high THz” frequencies, the need in a larger IF bandwidth becomes more pressing since the same velocity resolution for a Doppler shifted line at 5 THz requires a 5-times greater IF bandwidth than at 1 THz. Our work is focusing on the realization of practical HEB mixers using ultrathin (10-20 nm) MgB2 films. They are prepared using a Hybrid Physical-Chemical Vapor Deposition (HPCVD) process yielding ultrathin films with critical temperature ~ 37-39 K. The expectation is that the combination of small thickness, high acoustic phonon transparency at the interface with the substrate, and very short electron-phonon relaxation time may lead to IF bandwidth ~ 10 GHz or even higher. SiC continues to be the most favorable substrate for MgB2 growth and as a result, a study has been conducted on the transparency of SiC at THz frequencies. FTIR measurements show that semi-insulating SiC substrates are at least as transparent as Si up to 2.5 THz. Currently films are passivated using a thin (10 nm) SiO2 layer which is deposited ex-situ via RF magnetron sputtering. Micron-sized spiral antenna-coupled HEB mixers have been fabricated using MgB2 films as thin as 10 nm. Fabrication was done using contact UV lithography and Ar Ion milling, with E-beam evaporated Au films deposited for the antenna. Measurements have been carried out on these devices in the DC, Microwave, and THz regimes. The devices are capable of mixing signals above 20 K indicating that operation may be possible using a cryogen-free cooling system. We will report the results of all measurements taken to indicate the local oscillator power requirements and the IF bandwidth of MgB2 HEB mixers.
    SPIE Astronomical Telescopes + Instrumentation; 07/2014
  • [Show abstract] [Hide abstract]
    ABSTRACT: Local oscillator (LO) sources with sufficient output power are indispensable modules in submillimeter wave heterodyne detectors. In this work, we report on the design and characterization of a ×6×2 frequency multiplier chain that covers 176-196 GHz band. The LO chain mainly includes a W-band active times-6 frequency multiplier, a commercial W-band isolator, a W-band power module, a W-band band-pass filter (BPF) and a varactor-based G-band power-combined frequency doubler. First of all, design and performance of the W-band sextupler (×6), power module and BPF are briefly introduced. This is followed by a detailed description of the G-band frequency doubler as the key content. The final stage doubler employs two 50 μm thick quartz circuits and two commercially available varactor diodes. A circuit scheme named power-combining frequency multiplication is used for the doubler design. This circuit scheme is able to double the power handling capability of the frequency multiplier compared to the un-combined one. Therefore, the final stage doubler can fully make use of the driving power delivered by the power module to increase the output power. Each module is fabricated and assembled, and the discrete modules and the cascaded chain are measured, respectively. At room temperature, when pumped with 0 dBm at Ku-band, the LO chain produces at least 12.5 dBm in the 172-196 GHz band with a measured peak power of 16 dBm at 178 GHz. This power level is sufficient to pump a 0.36 THz heterodyne detector and makes it possible to deploy multi-pixel heterodyne imaging arrays in this frequency range.
    Journal of infrared, millimeter and terahertz waves 05/2015; 36(5). DOI:10.1007/s10762-015-0151-y · 1.89 Impact Factor