Nanopatterning and Hot Spot Modeling of YBCO Ultrathin Film Constrictions for THz Mixers

Abstract

International audienceHigh-T-C hot electron bolometers (HEB) are promising THz mixers due to their expected wide bandwidth, large mixing gain, and low intrinsic noise. To achieve this goal, 0.6-mu m-size constrictions were patterned on YBaCuO-based, 10-40-nm-thick films grown on (100) MgO substrates, which as previously reported, exhibited good DC superconducting properties. In this paper, we have simulated the DC and mixer characteristics of YBaCuO HEBs with a hot spot model usually dedicated to low-T-C devices. For a 100 nm x 100 nm x 10 nm constriction, the expected double sideband noise temperature T-N is 2000 K for 5 mu W local oscillator (LO) power (G = -13.5 dB conversion gain). For a larger (but more realistic according to YBaCuO aging effects) 600 nm x 1000 nm x 35 nm constriction, T-N = 1300 K at 200 mu W LO power (G = -12 dB). This approach is expected to allow optimizing the operation of the HEB constriction coupled to a THz planar antenna

YBCO-Constriction Hot Spot Modeling: DC and RF Descriptions for HEB THz Mixer Noise Temperature and Conversion Gain

“…The overall performance would degrade for α < 1, the best working point remaining the same. In particular, a T DSB ∝ exp(0.32f ) trend is obtained up to 2.5 THz, similar to the exp(0.4f ) experimental trend for Nb and NbN HEBs, as deduced from data reported in [12].…”

“…Besides, as already mentioned in [25], and considered in [12], [16], the bias current dependence of the critical temperature-with critical exponent γ-has also been accounted for in this study.…”

“…1, and write the thermal exchange in the device as governed by the heat equations pertaining to the electrons (1) and phonons (2) of the YBCO film, bearing indices e and p, respectively. In contrast with our initial formulation in [12], we introduce a full treatment of the phonon temperature and consider, as in [16], that it is not possible to neglect the phonon heat diffusion in high-T C materials (second order derivative in (2)). Moreover, we introduce a local source term in (1) to express the nonuniformity of both DC and RF power dissipation along the constriction length.…”

“…They evolved to a more complete (1-D) heat distribution picture that described the occurrence of dissipative regions-or hot spots-within the superconducting material; this hot spot model was primarily introduced for low-T C [11] and, more recently, for high-T C [12] mixers. Although seemingly accurate, the hot spot model does not totally reflect the fact that the mixing performances usually deteriorate at increasing radiofrequency (RF).…”

Superconducting high-Tc hot electron bolometers used as THz mixers: Predicted performance by hot spot modeling

“…From the T e (x) variation, the local YBCO resistivity ρ(x) could be deduced from the measured R(T) resistive superconducting transition as a reference [7], hence the I-V device DC characteristic [6]. An example is shown in Fig.…”