Normal-Metal Hot-Electron Nanobolometer With Johnson Noise Thermometry Readout

Abstract

The sensitivity of a THz hot-electron nanobolometer (nano-HEB) made from a normal metal is analyzed. Johnson Noise Thermometry (JNT) is employed as a readout technique. In contrast to its superconducting Transition-Edge Sensor (TES) counterpart, the normal-metal nano-HEB can operate at any cryogenic temperature depending on the required radiation background limited Noise Equivalent Power (NEP). It does not require bias lines; 100s of nano-HEBs can be read by a single low-noise <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$X$</tex> </formula> -band amplifier via a filter bank channelizer. The modeling predicts that even with the sensitivity penalty due to the amplifier noise, an <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm NEP}{\sim} 10^{-20}{\hbox{--}}10^{-19}{\hbox{W/Hz}}^{1/2}$</tex> </formula> can be expected at 50–100 mK in 10–20 nm thin titanium (Ti) normal metal HEBs with niobium (Nb) contacts. This NEP is fairly constant over a range of readout frequencies <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\sim$</tex></formula> 10 GHz. Although materials with weaker electron-phonon coupling (bismuth, graphene) do not improve the minimum achievable NEP, they can be considered if a larger than 10 GHz readout bandwidth is required.