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IEEE Transactions on Applied Superconductivity

Distributed quasiparticle mixing in a non-linear transmission line at sub-millimeter wavelengths

Edward Tong, R. Blundell, B. Bumble, J. A. Stern, Henry George LeDuc

Published Jun 1, 1997• 7 citations
Publisher

Abstract

A new class of distributed mixer based on the non-linear quasiparticle tunnel current in a superconductor-insulator-superconductor transmission line has been proposed and tested. The Nb/Al/AlOx/Nb junctions used in our mixers are typically 200 nm wide and are between 1 and 2 guided wavelengths long. Compared with the traditional sub-millimeter lumped element quasiparticle mixer, the distributed mixer requires lower critical current densities, lower magnetic field as well as simpler tuning circuitry. Experiments have been performed in various sub-millimeter frequency bands. Receiver noise temperatures of 66 K at 460 GHz, 210 K at 630 GHz and 600 K at 780 GHz have been measured. These noise temperatures are comparable to or slightly better than the noise temperatures of the corresponding lumped element mixers.

DOI
10.1109/77.622181

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A new class of distributed mixer based on the non-linear quasiparticle tunnel current in a superconductor-insulator-superconductor transmission line has been proposed and tested. The Nb/Al/AlOx/Nb junctions used in our mixers are typically 200 nm wide and are between 1 and 2 guided wavelengths long. Compared with the traditional sub-millimeter lumped element quasiparticle mixer, the distributed mixer requires lower critical current densities, lower magnetic field as well as simpler tuning circuitry. Experiments have been performed in various sub-millimeter frequency bands. Receiver noise temperatures of 66 K at 460 GHz, 210 K at 630 GHz and 600 K at 780 GHz have been measured. These noise temperatures are comparable to or slightly better than the noise temperatures of the corresponding lumped element mixers.
The non-linear quasiparticle current flowing in a superconductor- insulatorsuperconductor (SIS) transmission line has successfully been used in low-noise heterodyne receivers at sub-millimeter wavelengths. These distributed mixer receivers have been implemented in both the 400 and the 600 GHz frequency bands and double-side-band receiver noise temperatures of 66 K at 455 GHz and 210 K at 630 Gliz have been measured. Such performance is comparable to, or slightly better than the corresponding lumped element 515 mixerreceivers. The transmission lines used are fabricated from Nb/Al/A10x/Nb trilayer material, and are typrically 200 nm wide and 1-2 Ag long. The distributed mixer chips have been designed with a simple linear model. We present design rules derived from this model and discuss some difficulties in mixer implementation.
A non-linear superconducting transmission line has been successfully employed in heterodyne detection of sub-millimeter waves. In our experiments an Nb/Al/AlOx/Nb tunnel junction, measuring 0.15×40 μm, with a critical current density of about 2500 A/cm2 is used as a distributed mixer element. We have demonstrated that quantum limited sensitivity can be achieved with this type of device. At 460 GHz, a Y-factor of 2.5 has been recorded, corresponding to a double-side-band receiver noise temperature of 80 K. The double-side-band conversion loss is about 1 dB and the mixer noise temperature is estimated to be 18(±10) K.
The non-linear quasiparticle tunnel current flowing in a distributed superconductor-insulator-superconductor (SIS) transmission line resonator has been exploited in a low-noise heterodyne fixed-tuned waveguide receiver in the 600-720 GHz band. The mixer employs two 1.4 /spl mu/m wide half-wave or full-wave distributed SIS long junctions that are connected in series. These devices have been fabricated with optical lithography. Noise temperatures of 160-240 K have been measured at around 600 GHz. However, the achieved RF bandwidth is only about 5 % and the center frequency of the resonance is also shifted towards lower end of the target frequencies.
Quantum-limited mixer noise temperature has been achieved in Superconductor-Insulator-Superconductor (SIS) resonant mixer in the 600 — 720 GHz frequency range. Our mixer employs a single full-wave Nb/A1N/Nb tunnel junction resonator, fed by a quarter-wave transformer. The devices have low critical current density (-5 kA/cm 2 ). The mixers were tested in a fixed-tuned waveguide mixer mount. Double-side-band receiver noise temperatures equivalent to a few quanta have been measured for a number of different devices. Using a 0.55 x 25 Inn resonator, a noise temperature of 141 K was recorded at an LO frequency of 700 GHz with the mixer at 4.2 K. The noise temperature dropped to 111 K when the helium bath was pumped down to 2.8 K. High sensitivity has attained over reasonably wide RF bandwidth, —17%. The IF bandwidth of these mixers has also been investigated.
Superconductor–insulator–superconductor (SIS) mixers remain the choice of heterodyne mixers for single-dish telescopes and interferometers at millimeter and submillimeter wavelengths. Compared with conventional Nb/AlOx/Nb superconducting tunnel junctions, Nb/AlN/NbN ones have larger gap voltage and may reach critical-current density beyond 10kA/cm2, which are both of particularly interest in developing broadband SIS mixers. Here we report on the design and measurement of an SIS mixer based on Nb/AlN/NbN parallel connected twin junctions (PCTJ) incorporating NbTiN/SiO2/Al microstrip circuit. The junctions have a gap voltage of 3.18mV and a critical-current density of 15kA/cm2. The measured receiver noise temperature reach 5hν/kB among 200-260GHz band, and the mixer’s fractional bandwidth is about 40% centered at 230GHz.