Development of technology for manufacturing NbN HEB mixers with a small spread of DC and RF parameters for the creation of matrix receivers in the terahertz range

The work is devoted to an experimental study of the influence of the process parameters of magnetron deposition of a thin 4–5 nm superconducting film of niobium nitride NbN and the fabrication technology of NbN HEB mixers on the spread of their main parameters to minimize this spread in the future. The main parameters of the NbN HEB mixer are normal resistance R300, critical temperature $Tc$, superconducting transition width $T_c$, noise temperature $T_n$, conversion bandwidth B and required local oscillator power Pobs. Studies of B and current-voltage IV characteristics of NbN HEB mixers were carried out at different temperatures of the Si substrate, at $T$ near $T_c$ and $T$ much lower than $T_c$, this made it possible to identify individual interfaces in the mixer due to their different Tc. and study their influence. The uniformity of parameters of NbN HEB mixers, in addition to optimizing the NbN film deposition process, was achieved by preparing the surface of the Si substrate, as well as by using an Au layer deposited in situ with the NbN film – contact with a planar THz antenna. The NbN HEB mixers manufactured according to the optimized route had almost identical $R(T)$ characteristics with a spread of $T_c$ and normal resistance R300 of no more than 0.15 K and 2$\Omega$, respectively. The noise temperature at the local oscillator frequency of 2.52 THz was 800 K with a variation of 150 K from device to device. The noise bandwidth of the mixers at $T$ = 4.5 K averaged 7 GHz. Optimized fabrication technology will make it possible in the future to create multi-pixel heterodyne arrays from NbN HEB mixers with high uniformity of pixel parameters.