Since several years waveguide and planar antenna mixers with Nb-tunnel junctions are developed at the Space Research Organization Netherlands (SRON) for space applications. Recent results show excellent mixing performance up to frequencies above the superconducting gap of Nb. Goal is the development of an 1THz-mixer. Best results show a receiver noise temperature of Tps,-----310K at 708GHz for a waveguide mixer and TE,s„---200K at 480GHz for a double dipole planar antenna mixer. Due to on-chip tuning structures we obtained bandwidths up to 150GHz. We will present the current status in the development of SIS-junctions, integrated tuning network and mixers.
Since several years waveguide and planar antenna mixers with Nb-tunnel junctions are developed at the Space Research Organization Netherlands (SRON) for space applications. Recent results show excellent mixing performance up to frequencies above the superconducting gap of Nb. Goal is the development of an 1THz-mixer. Best results show a receiver noise temperature of Tps,-----310K at 708GHz for a waveguide mixer and TE,s„---200K at 480GHz for a double dipole planar antenna mixer. Due to on-chip tuning structures we obtained bandwidths up to 150GHz. We will present the current status in the development of SIS-junctions, integrated tuning network and mixers.
Since several years waveguide and planar antenna SIS-mixers for space applications are developed at SRON in orderof ESA. Recent results show excellent mixer performance up to frequencies above the superconducting gap of Nb.Goal is the development of a 1THz-mixer. Best results show a receiver noise temperature of Taw=400K at 720GHz incase of the waveguide mixer and T„„=200K at 490GHz for the double dipole planar antenna mixer. We will presentthe status in the development of SIS-junctions, integrated tuning network, mixers and mounts.
Heterodyne mixers based on superconducting SIS (superconductor-insulator-superconductor) tunnel junctions have been demonstrated to be the most sensitive coherent detectors at millimeter and submillimeter wavelengths. In fact, conventional superconducting SIS mixers with Nb/AlOx/Nb junction and Nb/SiO2/Nb tuning circuit have shown good performances with the noise temperature reaching as low as three times the quantum limit below 0.7THz, which is the gap frequency of Nb-based SIS junctions. However, due to the large loss in Nb thin-film superconducting microstrip lines, the noise performance of Nb SIS mixers deteriorates significantly above 0.7THz. With a gap frequency double that of Nb-based SIS junctions, NbN-based SIS junctions are of particular interest for the development of heterodyne mixers in the terahertz region. Considering the bandwidth and output power of local-oscillator (LO) signal sources are quite limited around 1THz, we firstly develop a waveguide NbN-based SIS mixer at 0.5THz. Three types of SIS junctions, i.e., long junction, parallel-connected tunnel junction (PCTJ) and distributed junction array (DJ) are investigated. They are all comprised of NbN-AlN-NbN tri-layer fabricated on an MgO substrate and have the same current density (Jc) of 10kA/cm2. In this paper, we describe their design, fabrication and preliminary experimental results.
Introduction Recently demonstrated integrated receiver [1] comprising a planar-antenna SIS mixer and a superconducting local oscillator based on FFO (Flux-Flow Oscillator), is limited in its frequency range by the SIS mixer as well as by the FFO. The coupling between FFO and mixer determines the effective bandwidth and could potentially be several hundreds of GHz. Recent development of all-Nb superconducting integrated receivers has demonstrated that the frequency of a single FFO can be tuned from 200 to 700 GHz [1],[2], i.e. up to the gap frequency of Nb. If the material with higher gap frequency (NbN for example) is used, the FFO can be running up to nearly two times this frequency, so up to 1200 GHz. However, the coupling of signal into SIS mixers with Nb tuning structures is found to be decreased rapidly above the gap frequency (about 700 GHz for Nb). This problem can be solved by using a normal metal such as aluminium for the coupling structures [3], [4]. In this contribution we present both calculated and experimental results of Nb-based SIS mixers in combination with a double dipole planar antenna for the highest possible frequencies. Special attention is paid
We report on the continuing development of submillimeter quasi-optical slot antenna SIS mixers which use two-junction tuning circuits [1]. The mixers use 10 kA/cm2 Nb/Al-Oxide/Nb junctions and Nb wiring, and have generated DSB receiver noise temperatures around 5hv/kB to 700 GHz, and 16hv/kB (620 K) at 798 GHz. We present Fourier-transform spectrometer (FTS) measurements and heterodyne measurements on several such devices. In general, the measured response at frequencies below the gap of Nb is in good agreement with the predicted performance. Introduction SIS mixers with Nb-trilayer tunnel junctions offer excellent performance at frequencies below 800 GHz, and should perform competitively at frequencies as high as 1.4 THz [2-5]. Our goal is to develop a suite of ultra-low-noise SIS mixers which cover frequencies from = 400 GHz to more than I THz. At frequencies below the Nb gap (< 700 GHz), existing devices perform quite well [6], but further improvements in noise temperatures remain important. In addition, it is quite useful to be able to predict device performance given the design parameters. One can then optimize the device design for a particular frequency band, and confirm that we indeed understand the physics of the device. Progress in the design and operation of devices in this frequency range is presented below. At frequencies above the Nb gap, RF photons can break Cooper pairs, resulting in greater signal loss and higher receiver noise temperatures. The loss is particularly important in the slender microstrip lines used to resonate the junction capacitance and to transform the antenna impedance down to the RF junction impedance. However, the actual coupling of radiation into Nb junctions above the gap should still be reasonably efficient -more than 30% at 800 GHz [7]. In addition to RF loss, one is also affected by increased dispersion at frequencies near the gap. The Nb microstriplines have therefore been carefully designed to ensure the desired bandpass is achieved. We demonstrate for the first time that all-Nb SIS receivers can have substantially better performance than GaAs Schottky receivers for the astronomically important CI ( P2 — P 1 ) and CO (7-6) transitions near 810 GHz. Receiver Configuration Since waveguide mixers become difficult to construct at short submillimeter wavelengths, we have adopted a quasi-optical approach. Here, lenses take the place of waveguide horns, and the incoming radiation is collected by a planar antenna on the SIS mixer substrate [8]. This offers several other advantages, such as on-chip broad-band silt a SS 114 SSE WA Wa Sta MX Dewar 120 Mylar Window SIS Mixer 295 IQ 77 K Mylar Load Bearnsplitter ICI 1= NZ IC =1 HEN1T Amplifier Polyethylene Lens
Heterodyne mixers based on superconducting SIS (superconductor-insulator-superconductor) tunnel junctions have been demonstrated to be the most sensitive coherent detectors at millimeter and submillimeter wavelengths. In fact, conventional superconducting SIS mixers with Nb/AIO(x)/Nb junction and Nb/SiO2/Nb tuning circuit have shown good performances with the noise temperature reaching as low as three times the quantum limit below 0.7THz, which is the gap frequency of Nb-based SIS junctions. However, due to the large loss in Nb thin-film superconducting microstrip lines, the noise performance of Nb SIS mixers deteriorates significantly above 0.7THz. With a gap frequency double that of Nb-based SIS junctions, NbN-based SIS junctions are of particular interest for the development of heterodyne mixers in the terahertz region.
This thesis investigates the prospects of some different superconducting mixers integrated with planar antennas for the millimeter and submillimeter regime. Two kinds of Superconductor/Insulator/Superconductor (SIS) tunnel junctions for use in mixers have been fabricated; Nb/PbBi edge junctions and Nb trilayer junctions. One of the very high quality trilayer mixers is currently operating in a 350 GHz radio-telescope heterodyne-receiver. The reduced sensitivity of SIS mixers for frequencies above the gap frequency (?700 GHz) of the superconductors has directed the interest towards another type of superconducting mixer device, the superconducting Hot Electron Bolometer (HEB). Various types of this device have been studied; Nb devices for scale-measurements at 20 GHz to more easily verify some of the theoretical background of the HEB, NbN waveguide devices for 100 GHz, and NbN devices integrated with planar antennas for a quasi-optical mixer at 350 GHz. Two types of planar antennas have been used; the endfire "Broken" Linearly Tapered Slotline Antenna (BLTSA) on a thin dielectric membrane, and the double dipole antenna on a quartz substrate lens. The beam pattern of the BLTSA has been examined theoretically and measured at 40 GHz with antennas supported by Kapton foil, and at 350 and 800 GHz with antennas on thin dielectric SiOxNy membranes. Measurements of the 20 GHz Nb HEB show a mixer conversion loss close to 0 dB for IF frequencies below 40 MHz. The maximum IF bandwidth given by the electron temperature relaxation time corresponds to a frequency of about 80 MHz. A DSB mixer noise temperature of only a few hundred Kelvin has been measured. Corresponding measurements of NbN devices at 100 and 350 GHz give a mixer conversion loss of about 6-10 dB and an IF bandwidth of about 700 to 1000 MHz. The output noise is found to be dominated by electron temperature fluctuations with an equivalent noise temperature of about 100 K, and a frequency dependence equal to that of the IF signal. Phenomenological expressions for conversion loss, noise, and IF impedance have been compared measurements and shows good agreement. The quasioptical NbN HEB mixers are still under development with respect to film quality and coupling to radiation, why the mixer performance of these is expected to improve.