Noise Measurements in Ti Hot-Electron Nanobolometers

Alexander A. Verevkin, Irfan A. Siddiqi, D. E. Prober +5 more

Boris S. Karasik, David I. Olaya, Jian Wei +5 more

We are developing hot-electron superconducting transition-edge sensors (TES) capable of counting THz photons and operating at . We fabricated superconducting Ti nanosensors with Nb contacts with a volume of on planar Si substrates and have measured the thermal conductance in the material, G=4times10-3W/K at 0.3 K, caused predominantly by the weak electron-phonon coupling. The corresponding phonon-noise NEP=3times10-19W/Hz1/2. Detection of single optical photons (1550 nm and 670 nm wavelength) has been demonstrated for larger devices and yielded the thermal time constants of 30 mus at 145 mK and of 25 mus at 190 mK. This hot-electron direct detector (HEDD) is expected to have a small enough energy fluctuation noise for detecting individual photons with v>THz where NEP~3times10-20W/Hz1/2is needed for spectroscopy in space.

Boris S. Karasik, Peter K. Day, Jonathan H. Kawamura +5 more

We have obtained the first data on the multiplexed operation of titanium hot‐electron bolometers (HEB). Because of their low thermal conductance and small electron heat capacity nanobolometers are particularly interesting as sensors for far‐infrared spectroscopy and mid‐ and near‐IR calorimetry. However, the short time constant of these devices (∼μs at 300–400 mK) makes time domain or audio‐frequency domain multiplexing impractical. The Microwave SQUID (MSQUID) approach pursued in this work uses dc SQUIDs coupled to X‐band microresonators which are, in turn, coupled to a transmission line. We used a 4‐element array of Ti HEBs operated at 415 mK in a He3 dewar with an optical fiber access. The microwave signal exhibited 10‐MHz wide resonances at individual MSQUD frequencies between 9 GHz and 10 GHz. The resonance depth is modulated by the current through the bolometer via a change of the SQUID flux state. The transmitted signal was amplified by a cryogenic amplifier and downconverted to baseband using an IQ mixer. A 1‐dB per Ω0/2 responsivity was sufficient for keeping the system noise at the level of ∼2 pA/Hz1/2. This is more than an order of magnitude smaller than phonon noise in the HEB. The devices were able to detect single near‐IR photons (1550 nm) with a time constant of 3.5 μs. Follow‐on work will scale the array to larger size and will address the microwave frequency signal generation and processing using a digital transceiver.

Dibyendu Hazra, Joonas Govenius, Russell E. Lake +16 more

Boris S. Karasik, Sergei V. Pereverzev, David I. Olaya +3 more

We are presenting experimental results on the electrical noise in small titanium hot-electron nanobolometers with the critical temperature above 300 mK. The noise data demonstrate good agreement with the conventional bolometer theory prediction. The noise is dominated by the thermal energy fluctuations (phonon noise) when the operating temperature is set just a few mK below the superconducting transition. The corresponding noise equivalent power (NEP) is about 3 times 10-18W/Hz1/2for the smallest measured device. The relative NEP's for the two devices measured scale roughly as the square root of the device volume as one would expect from the theory. Therefore an additional factor of 2-3 reduction of NEP may be feasible if the length and width of our device are further reduced. The demonstrated combination of the low NEP and the relatively high operating temperature is attractive for submillimeter low-background applications.

Göran Johansson, Per Delsing, Kevin Bladh +5 more