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Hot-electron bolometers (HEBs) based on Johnson noise thermometry are potential terahertz detectors with high sensitivity and wide dynamic range. Understanding the thermal conductance of these detectors is crucial, as their sensitivity scales linearly with this property. In this paper, we focus on the experimental study of the thermal conductance of the titanium HEBs with different microbridge thicknesses ranging from 15 to 59 nm. We find that the thermal conductance of the HEBs takes a temperature power law of Tn, and the exponent n decreases from 3.4 to 2.8 as the microbridge thickness increases. The variation of the exponent n is mainly due to electron diffusion, which is not completely suppressed by superconducting contacts and is stronger in thick microbridges. In addition, we observed that the thermal radiation from the low-noise amplifier for Johnson noise readout may raise the electron temperature by about 30 mK at the bath temperature of 0.25 K, giving an excessive thermal conductance. [ABSTRACT FROM AUTHOR]

Graphene hot-electron bolometer (HEB) detectors, with weak electron–phonon interaction and a wide working temperature range, are of particular interest for terahertz (THz) applications including astronomy. In this paper, we report on the performance of a zero-biased THz HEB detector using Johnson noise thermometry based on bilayer graphene (BLG) of high charge carrier density. Two BLG HEB devices with respective normal-metal and superconducting electrodes are compared particularly for their thermal conductance and detection sensitivity (noise equivalent power, NEP) in a low-temperature regime (0.3–10 K). With electron out-diffusion largely suppressed by Andreev reflection, the device with superconducting electrodes outperforms the device with normal-metal electrodes, giving an electrical NEP of 15 fW/Hz0.5 and a dynamic range of 47 dB at 0.3 K. Moreover, its optical coupling efficiency is found to be 58% and can reach as high as 92% with the optical losses of the measurement system calibrated out. Graphene detectors of this kind can achieve better detection performance given lower readout noise and decreased electron–phonon thermal conductance. [ABSTRACT FROM AUTHOR]

A hot electron bolometer (HEB) with Johnson noise readout is an attractive technique for radiation detection due to its high sensitivity, wide operating temperature range, and large dynamic range. In this paper, we present the development of a terahertz HEB based on Johnson noise readout. The HEB consists of a titanium microbridge connected to two high-energy-gap niobium contacts for confining hot electrons. We measured the thermal conductance and noise equivalent power (NEP) of the HEB at different bath temperatures. We find that the thermal conductance due to the electron–phonon interaction increases with temperature as T2.5. At 3.0 K, the thermal conductance is found to be 37.9 ± 1.4 nW/K and the electrical NEP is as low as 23.0 ± 0.8 pW/ Hz . In addition, we find that the HEB works efficiently up to 15 μW input power. [ABSTRACT FROM AUTHOR]

We interpret the experimental observation of a frequency-dependence of superconducting hot electron bolometer (HEB) mixers by taking into account the non-uniform absorption of the terahertz radiation on the superconducting HEB microbridge. The radiation absorption is assumed to be proportional to the local surface resistance of the HEB microbridge, which is computed using the Mattis-Bardeen theory. With this assumption the dc and mixing characteristics of a superconducting niobium-nitride (NbN) HEB device have been modeled at frequencies below and above the equilibrium gap frequency of the NbN film. [ABSTRACT FROM AUTHOR]

We are developing a detection system based on a NbSi Transition Edge Sensor (TES) bolometer array. A thermo-mechanical architecture accomodates the array and the cryogenic stage of the readout. We model the coupling of the TES bolometer to the radiation by means of twin slot antenna. We present the latest design of the cryogenic readout which includes a BiCMOS SiGe integrated circuit at 4 K controlling a Superconducting Quantum Interference Device (SQUID) amplifier. [ABSTRACT FROM AUTHOR]

In this paper we study the temperature dependence of the receiver noise temperature and IF noise bandwidth of superconducting hot electron bolometer (HEB) mixers. Three superconducting NbN HEB devices of different transition temperatures (Tc) are measured at 0.85 THz and 1.4 THz at different bath temperatures (Tbath) between 4 K and 9 K. Measurement results demonstrate that the receiver noise temperature of superconducting NbN HEB devices is nearly constant for Tbath/Tc, less than 0.8, which is consistent with the simulation based on a distributed hot-spot model. In addition, the IF noise bandwidth appears independent of Tbath/Tc, indicating the dominance of phonon cooling in the investigated HEB devices. [ABSTRACT FROM AUTHOR]