Superconducting transition edge sensors with phononic thermal isolation

Abstract

The sensitivity of a low-noise superconducting transition edge sensor (TES) is determined by the thermal conductance of the support structure that connects the active elements of the device to the heat bath. Lownoise devices require conductances in the range 0.1 to 10 pW K −1 , and so have to rely on diffusive phonon scattering in long, narrow, amorphous SiN x legs. We show that it is possible to manufacture and operate TESs having short, ballistic low-dimensional legs (cross section 500 × 200 nm) that contain multi-element phononic interferometers and ring resonators. These legs transport heat in effectively just 5 elastic modes at the TES's operating temperature (< 150 mK), which is close to the quantised limit of 4. The phononic filters then reduce the thermal flux further by frequency-domain filtering. For example, a micromachined 3-element ring resonator reduced the flux to 19 % of a straight-legged ballistic device operating at the quantised limit, and 38 % of a straight-legged diffusive reference device. This work opens the way to manufacturing TESs where performance is determined entirely by filtered, few-mode, ballistic thermal transport in short, low-heat capacity legs, free from the artifacts of two level systems. arXiv:1805.09783v1 [cond-mat.mes-hall]

Thermal kinetic inductance detectors for millimeter-wave detection

“…Even lower thermal conductances down to 0:1 pW/K can be achieved by incorporating phononic thermal filters in the thermal link design. 58 TKID bolometers can, therefore, be implemented under a wide range of potential loading conditions. The bolometer time constant, τ bolo ¼ C(T o )=G(T o ), sets the bandwidth of the device.…”

Transition-edge sensor detectors for the Origins Space Telescope

“…66,68,69 "Phononic filter bolometers" use nanomachined legs to generate coherent phonon scattering that suppresses propagated phonon modes to below the quantum limit. 34,[68][69][70] Like ballistic leg bolometers, phononic filter bolometers promise short legs that enable high array filling fractions but with the additional advantage of reduced thermal conductivity relative to ballistic leg designs. Theoretical work by Rostem et al 68 indicates that a factor of 5 improvement over the quantum limit is possible with phononic filter legs that are just 10 μm long and are machinable using known techniques.…”

“…Theoretical work by Rostem et al 68 indicates that a factor of 5 improvement over the quantum limit is possible with phononic filter legs that are just 10 μm long and are machinable using known techniques. Devices presented by Williams et al 69 achieved a factor of ∼2 reduction in thermal conductance below the quantum limit using phononic filter legs. Fabrication of phononic filters is challenging as submicrometer lithography techniques are required, but recent work by Denis et al 71 demonstrates the reliable and robust fabrication of phononic leg-isolated TESs.…”

“…Compared to long-legged bolometers, ballistic leg bolometers can achieve much higher array fill fractions, and the achieved thermal conductance of realized legs is both calculable from real bulk material properties and is much more tolerant of fabrication non-idealities and nonuniformities. 66,68,69 Phononic filter bolometers use nano-machined legs to generate coherent phonon scattering that suppresses propagated phonon modes to below the quantum limit. 34,[68][69][70] Like ballistic leg bolometers, phononic filter bolometers promise short legs that enable high array filling fractions, but with the additional advantage of reduced thermal conductivity relative to ballistic leg designs.…”

Thermal Kinetic Inductance Detectors Camera: System Level Design, Strategy and Performance Forecast

“…The phonons on the island alter the number of quasiparticle in the inductive element L and are dissipated via the island suspensions or legs, P leg . The thermal conductance of the legs G can be tuned during the fabrication process [15]. The resonator properties changes are detected using a probe signal with power coming from the room temperature readout electronics, P read source.…”