Microwave mixing in microbridges made from YBa2Cu3O7−x thin films

Abstract

We present a systematic study of the response of a YBa 2 Cu 3 O 7Ϫx thin-film microbridge to millimeter wave radiation. The dependencies of the microwave response spectrum on the bias voltage and operating temperature have been measured on samples made from YBa 2 Cu 3 O 7Ϫx films with different thicknesses. Once the bias voltage exceeds the value corresponding to the first maximum of differential resistance, the value of the Ϫ3 dB roll-off frequency of the microbridge response is drastically reduced. On the other hand, at temperatures close to T c the roll-off frequency rises to about 20 GHz. For high resistivity YBa 2 Cu 3 O 7Ϫx films with relatively low upper critical magnetic fields the Ϫ3 dB roll-off frequency is about 7 GHz even at temperatures much smaller than T c . To explain the results obtained we consider the presence of two additive mechanisms that contribute to the YBa 2 Cu 3 O 7Ϫx thin-film microbridge response to microwave radiation: vibration of magnetic vortices and heating of electrons and phonons. The competition between these two mechanisms defines the bias voltage and temperature dependencies of the Ϫ3 dB roll-off frequency as well as the recently reported dependence of the intermediate frequency bandwidth of YBa 2 Cu 3 O 7Ϫx hot-electron bolometer mixers on the local oscillator frequency. Numerical calculations based on this assumption are in a good qualitative agreement with the experimental results.

Influence of thickness, width and temperature on critical current density of Nb thin film structures

“…At low temperatures the penetration and movement of magnetic vortices can modify the current carrying ability of thin films of superconductors of the second type and the performance of devices made from these films. It has been found that the hot-electron bolometer (HEB) mixers made from low- [9] and high-T C [10] superconducting thin films demonstrate an increase of the intermediate frequency bandwidth at subTHz local oscillator frequency due to oscillations of the magnetic vortices. Nucleation and movement of the vortices is currently considered as a mechanism responsible for the generation of dark counts in the superconducting nanowire single-photon detectors (SNSPD) [11].…”

Superconducting YBa2Cu3O7−δ Thin Film Detectors for Picosecond THz Pulses

“…For YBCO film thicknesses above 30 nm T c is nearly constant and well above 77 K. For films thinner than 30 nm T c decreases significantly. This can be explained by the above-mentioned lattice mismatch leading to oxygen deficiency in the YBCO film, which results in a reduction of T c [13] down to 25 K for 15 nm thick films. The T c of films with d < 30 nm has been improved by a decrease of the CeO 2 layer thickness.…”

THz Mixing with High-TC Hot Electron Bolometers: a Performance Modeling Assessment for Y-Ba-Cu-O Devices

“…Besides, YBCO was attractive in several respects, e.g., operating temperature with light cryogenics, or fast response, due to its very short electron-phonon relaxation time τ ep , in the ps range [6][7][8]. Early YBCO HEB mixers were demonstrated at mm-wave [9][10][11][12] or THz [9,10,[13][14][15] frequencies. Difficulties were encountered, however, which mainly arose from YBCO chemical reactivity to atmospheric water and carbon dioxide and to the fabrication process as well, which compromised the durability of good performances for frequency mixing operation [16].…”

“…Difficulties were encountered, however, which mainly arose from YBCO chemical reactivity to atmospheric water and carbon dioxide and to the fabrication process as well, which compromised the durability of good performances for frequency mixing operation [16]. They also arose from the superconducting film to substrate phonon escape time τ esc , much longer for YBCO [17] than for Nb, for instance [18], with a detrimental effect on the instantaneous much longer for YBCO [17] than for Nb, for instance [18], with a detrimental effect on the instantaneous bandwidth [11][12][13]19]. More recently, MgB 2 has met a sustained interest as a compromise between NbN and YBCO, in terms of operating temperature, but also in terms of instantaneous bandwidth [20,21].…”