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IEEE Microwave and Guided Wave Letters

Superconducting bolometric mixers

H. Ekstrom, Boris S. Karasik, E. Kollberg, Sigfrid Yngvesson

Published Jul 1, 1994• 7 citations
Publisher

Abstract

Mixing at 20 GHz in niobium superconducting thin-film strips in the resistive state is studied. Experiments give evidence that electron-heating is the main cause of the nonlinear phenomena. The requirements on the mode of operation and on the film parameters for small conversion loss and the possibility of conversion gain are discussed. Measurements indicate a conversion loss between 1-8 dB and a DSB mixer noise temperature between 100 and 450 K at 20 GHz. The device output noise temperature at the mixer operating point can be as low as 30-40 K. A simple theory that is based on the assumption that the small signal resistance is linearly dependent on power is presented. This type of mixer is considered very promising for use in low-noise heterodyne receivers at THz frequencies.>

DOI
10.1109/75.298257

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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Dec 22, 1998•1 citation
Mixing at 20 GHz in niobium superconducting thin-film strips in the resistive state is studied. Experiments give evidence that electron-heating is the main cause of the nonlinear phenomena. The requirements on the mode of operation and on the film parameters for small conversion loss and the possibility of conversion gain are discussed. Measurements indicate a conversion loss between 1-8 dB and a DSB mixer noise temperature between 100 and 450 K at 20 GHz. The device output noise temperature at the mixer operating point can be as low as 30-40 K. A simple theory that is based on the assumption that the small signal resistance is linearly dependent on power is presented. This type of mixer is considered very promising for use in low-noise heterodyne receivers at THz frequencies.>
A study has been done of microwave mixing at 20 GHz using the nonlinear (power dependent) resistance of thin niobium strips in the resistive state. Our experiments give evidence that electron-heating is the main cause of the nonlinear phenomenon. Also a detailed phenomenological theory for the determination of conversion properties is presented. This theory is capable of predicting the frequency-conversion loss rather accurately for arbitrary bias by examining the I-V characteristic, Knowing the electron temperature relaxation time, and using parameters derived from the I-V-characteristic also allows us to predict the -3-dB IF bandwidth. Experimental results are in excellent agreement with the theoretical predictions. The requirements on the mode of operation and on the film parameters for minimizing the conversion loss (and even achieving conversion gain) are discussed in some detail. Our measurements demonstrate an intrinsic conversion loss as low as 1 dB. The maximum IF frequency defined for 3-dB drop in conversion gain, is about 80 MHz. Noise measurements indicate a device output noise temperature of about 50 K and SSB mixer noise temperature below 250 K. This type of mixer is considered very promising for use in low-noise heterodyne receivers at THz frequencies.>
The mixing of 20 GHz radiation in a Nb superconducting film in the resistive state was studied. The experiment gave evidence of electron-heating to be the origin of the non-linear phenomenon. The requirements on the operation mode and on the film parameters in order to obtain small conversion losses or even gain are determined. Our measurements indicate a conversion loss of about 6-8 dB. The hot-electron bolometer is considered to be very promising for use in heterodyne receivers in a wide frequency range from microwaves to terahertz frequencies.
Bolometric mixers based on Nb and NbN superconducting thin films in the resistive state have been prepared for 20, 100 GHz and 350-500 GHz operation. The mixing mechanism is presumably of electron heating origin. Our measurements indicate that a conversion loss of about 6-8 dB can rather easily be achieved, and that the noise is reasonably low. The requirements on the operation mode and on the film parameters in order to obtain small conversion losses or even gain are discussed. For NbN films the availability of nearly 1 GHz IF bandwidth is experimentally demonstrated. NbN hot-electron mixers combined with slot-line tapered antenna on Si membrane or with double-dipole antenna on SiO2 substrate have been fabricated. The devices we study are considered to be very promising for use in heterodyne receivers from microwaves to terahertz frequencies.
Mixing experiments have been performed at frequencies from 4 to 20 GHz on Nb thin-film superconducting hot-electron bolometers varying in length from 0.08 to 3 μm. The intermediate frequency (IF) bandwidth is found to vary as L−2, with L the bridge length, for devices shorter than √12 Le−ph≊1 μm, with Le−ph the electron-phonon length. The shortest device has an IF bandwidth greater than 6 GHz, the largest reported for a low-Tc superconducting bolometric mixer. The conversion efficiencies range from −5 to −11 dB (single sideband, SSB). For short bridges, the mixer noise temperature is found to be as low as 100 K (double sideband, DSB), with little length dependence. The local oscillator power required is small, ≊10 nW. Such mixers are very promising for low-noise THz heterodyne receivers.
A theory of an electron-heating mixer which makes it possible to calculate all the characteristics of the device is developed. It is shown that positive conversion gain is possible for such a mixer in the millimeter to near-infrared wavelength range. The dynamic range and the optimum heterodyne power can be selected from a very wide interval by varying the mixing element volume. Measurements made for Nb within the frequency range of 120-750 GHz confirm the theory. The conversion loss obtained at T=1.6 K and normalized to the element reaches 0.3 dB in the intermediate frequency band of 40 MHz; the possible noise temperature is 50 K. The estimation of noise temperature and output band for YBaCuO at T=77 yields 200 K and more than 10 GHz, respectively.
Small volume high-Tc super-conducting YBa2Cu3O7 (YBCO) thin films are used as low power, very wide bandwidth mixers in the frequency range of 75 GHz to 2.5 THz. The YBCO films are patterned into lattice-cooled hot-electron bolometers (HEB) coupled to an integrated Au thin-film antenna and transmission line. Near 77 K, these mixers have responsivity as high as 780 V/W using only 8 nW of local oscillator (LO) power at 585 GHz. The responsivity can be shown to be truly bolometric. Direct heterodyne and homodyne down-conversion mixing using local-oscillator frequencies of 75 GHz and 585 GHz show overall conversion gains of -35 dB, which includes a -18 dB coupling loss, using only approximately 1 (mu) W of LO power. The gain bandwidth shows a simple Lorentzian roll-off with -3 dB point of 5 to 8 GHz. The large gain bandwidth and small power requirements make these high-Tc superconducting mixers an attractive alternative to existing Schottky diode and conventional superconducting receiver technologies.