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IEEE Transactions on Applied Superconductivity

A heterodyne receiver at 533 GHz using a diffusion-cooled superconducting hot electron bolometer mixer

Anders J. Skalare, William R. McGrath, B. Bumble, Henry George LeDuc, Peter John Burke, A. A. Verheijen, D. E. Prober

Published Jun 1, 1995• 32 citations
Publisher

Abstract

This paper describes heterodyne measurements at 533 GHz using a novel superconducting hot electron bolometer in a waveguide mixer block. The bolometer is a thin (10 nm) and narrow (0.1 /spl mu/m) strip of niobium with a length of less than half a micron and a critical temperature of approximately 5.5 K. The short length ensures that diffusion dominates over electron-phonon interaction as a cooling mechanism for the hot electrons, thus allowing heterodyne detection with intermediate frequencies of several GHz. A Y-factor response of 1.15 dB has been obtained at an intermediate frequency of 1.4 GHz with hot/cold load temperatures of approximately 295/77 K, indicating a receiver noise temperature around 650 K DSB. The IF response extends up to at least 2 GHz and possibly higher.>

DOI
10.1109/77.403030

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Heterodyne measurements have been made at 533 GHz using a novel superconducting hot-electron bolometer in a waveguide mixer. The bolometer is a 0.3 μm long niobium microbridge with a superconducting transition temperature of 5 K. The short length ensures that electron diffusion dominates over electron-phonon interactions as the electron cooling mechanism, which should allow heterodyne detection with intermediate frequencies (if) of several GHz. A Y-factor response of 1.15 dB has been obtained at an if of 1.4 GHz with 77 and 295 K loads, indicating a receiver noise temperature of 650 K DSB. The −3 dB rolloff in the if response occurs at 1.7 GHz.

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We report on the first heterodyne measurements with a diffusion-cooled hot-electron bolometer mixer in the submillimeter wave band, using a waveguide mixer cooled to 2.2 K. The best receiver noise temperature at a local oscillator frequency of 533 GHz and an intermediate frequency of 1.4 GHz was 650 K (double sideband). The 3 dB IF roll-off frequency was around 1.7 to 1.9 GHz, with a weak dependence on the device bias conditions.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Oct 13, 1995•0 citations
This paper describes heterodyne measurements at 533 GHz using a novel superconducting hot electron bolometer in a waveguide mixer block. The bolometer is a thin (10 nm) and narrow (0.1 /spl mu/m) strip of niobium with a length of less than half a micron and a critical temperature of approximately 5.5 K. The short length ensures that diffusion dominates over electron-phonon interaction as a cooling mechanism for the hot electrons, thus allowing heterodyne detection with intermediate frequencies of several GHz. A Y-factor response of 1.15 dB has been obtained at an intermediate frequency of 1.4 GHz with hot/cold load temperatures of approximately 295/77 K, indicating a receiver noise temperature around 650 K DSB. The IF response extends up to at least 2 GHz and possibly higher.>
Heterodyne measurements have been made at 533 GHz using a novel superconducting hot-electron bolometer in a waveguide mixer. The bolometer is a 0.3 μm long niobium microbridge with a superconducting transition temperature of 5 K. The short length ensures that electron diffusion dominates over electron-phonon interactions as the electron cooling mechanism, which should allow heterodyne detection with intermediate frequencies (if) of several GHz. A Y-factor response of 1.15 dB has been obtained at an if of 1.4 GHz with 77 and 295 K loads, indicating a receiver noise temperature of 650 K DSB. The −3 dB rolloff in the if response occurs at 1.7 GHz.
We report on heterodyne mixing experiments between 630-820 GHz using a diffusion-cooled superconducting hot electron bolometer at intermediate frequencies from 1-2 GHz. The niobium bolometer which is cooled by diffusion of the hot electrons into a normal conductor has dimensions of 0.3 /spl mu/m/spl times/0.15 /spl mu/m and was fabricated at KOSMA with a two-step electron beam lithography process. The film thickness of the device is 30 nm with T/sub c/ of 6.1 K and /spl Delta/T/sub c/ of 0.7 K. The mixing experiments are performed with a tunerless waveguide mixer block previously used for very low-noise SIS receivers. At a physical temperature of 2.2 K, receiver noise temperatures at 666 GHz are 1500 K at 1.0 GHz intermediate frequency, increasing rapidly above 1.5 GHz. The dissipated local oscillator power is evaluated to be 65-90 nW.
We report on heterodyne measurements with a Nb diffusion-cooled hot-electron bolometer in a fixed tuned waveguide mixer at 700 GHz. The device is a 300 nm long and 12 nm thick Nb microbridge, with a normal state resistance of 31 Si. We have measured the DSB receiver noise temperature using a standard Y-factor method with a 300 K and 77 K blackbody load. At 700 GHz, a bath temperature of 4.3 K, and an intermediate frequency of 1.25 GHz, the receiver noise temperature Tre, ,DsB is 1690 K after correction for the losses in the beamsplitter. Reducing the bath temperature to 3.3 K decreases Trec.Dsg to 1100 K. Careful inspection of the pumped differential I(V) characteristics does not reveal any influence due to direct detection. From the data we extract a maximum value of —17.8 dB for the conversion gain of the mixer at 4.3 K. The minimum mixer noise is determined to be 1170 K by applying a noise breakdown calculation. We expect significant improvement of the receiver noise performance upon further reduction of the bath temperature.
We present microwave (30 GHz) measurements on aluminum superconducting hot-electron bolometer (HEB) mixers. Aluminum HEB mixers have a lower superconducting transition temperature than niobium and niobium nitride devices, and are predicted to have improved sensitivity and require less local oscillator power. The devices studied consist of a narrow superconducting aluminum microbridge with contacts comprised of thick aluminum, titanium, and gold. A perpendicular magnetic field is used to suppress superconductivity in the contacts. The device length is much shorter than the electron–phonon inelastic length [L≪(Dτe–ph)1/2] and thus the intermediate frequency (IF) bandwidth is set by the diffusion time of hot electrons from the microbridge into the contacts. We discuss limitations on the IF bandwidth in very short HEB mixers with fully normal contacts. Overall, the microwave heterodyne mixing results show good performance with a mixer noise temperature inferred from the conversion efficiency and output noise of TM⩾4 K, double side band (DSB). Measurements at 618 GHz yield a conversion efficiency approximately 10 dB lower than observed at 30 GHz. Output saturation by background radiation is postulated to contribute significantly to this difference. A similar decrease in conversion efficiency in the microwave mixing measurements is observed when broadband noise is added to the rf input signal. We discuss the tradeoff between increased sensitivity and the occurrence of saturation effects in low transition temperature HEBs.
In this paper we report receiver sensitivity measurements with a diffusion-cooled niobium hot-electron bolometer around 1100 GHz. The lowest receiver noise temperature was 1670 K DSB, with approximately 40 nW of local oscillator power being dissipated in the device. The intermediate frequency bandwidth of this device, due to its short length (0.15 gm) and low normal resistance (43 a), exceeded the 1.8 GHz bandwidth of the measurement setup. The receiver was used to detect the sulfur dioxide gas absorption line at 1102 GHz in a heterodyne mode.