Transition edge sensors with few-mode ballistic thermal isolation

Abstract

We have fabricated Transition Edge Sensors (TESs) whose thermal characteristics are completely characterised by few-mode ballistic phonon exchange with the heat bath. These TESs have extremely small amorphous SiN x support legs: 0.2 µm thick, 0.7 to 1.0 µm wide and 1.0 to 4.0 µm long. We show, using classical elastic wave theory, that it is only necessary to know the geometry and bulk elastic constants of the material to calculate the thermal conductance and fluctuation noise. Our devices operate in the few-mode regime, between 5 and 7 modes per leg, and have noise equivalent powers (NEPs) of 1.2 aW Hz −1/2 . The NEP is dominated by the thermal fluctuation noise in the legs, which itself is dominated by phonon shot-noise. Thus TESs have been demonstrated whose thermal characteristics are fully accounted for by an elastic noise-wave model. Our current devices, and second-generation devices based on patterned phononic filters, can be used to produce optically compact, mechanically robust, highly sensitive TES imaging arrays, circumventing many of the problems inherent in conventional long-legged designs.

Wide-stopband aperiodic phononic filters

“…The root-mean-square and correlation length in beam edge roughness are subdominant to the thermal wavelength at 100 mK by two orders of magnitude, λ th ∼ 2πhv/k B T , where v is the typical speed of sound of out-of-plane flexural modes in a dielectric (∼5000 m s −1 ). Hence, cooling phononic devices to sub-Kelvin temperature offers the opportunity to fully test and measure the coherent long-wavelength meta-material properties of these structures at the mesoscopic limit [17,3,18].…”

Electrothermal feedback in kinetic inductance detectors

“…In practice, the thermal isolation could be controlled by depositing the superconducting resonator on a membrane only connected to the bulk substrate by thin legs. This principle is already standard for other types of photon detectors such arXiv:1701.09145v1 [astro-ph.IM] 31 Jan 2017 as Transition Edge Sensors, 15,16 and is used in recent KID designs. [17][18][19] As the context of this work is using superconducting resonators as detectors, we investigate the effects of this thermal isolation on responsivity to signal power and noise.…”

“…Noise-equivalent signal power (NEP) in IQ output, contribution from intrinsic temperature fluctuations, along the directions of A (solid) and B (dashed) from(16) in the IQ plane, with and without the effects of electrothermal feedback. NEP peaks at the limits of the response bandwidth of the device.…”

THz spectroscopy of the atmosphere for climatology and meteorology applications

“…Although our demonstrator will target the frequency range 50-60 GHz, the underlying technology will be suitable for frequencies ranging from a few tens of GHz up to many hundreds of GHz, and for spectrometers having several hundred spectral channels. Each TES would comprise a MoAu bilayer on a 200 nm SiNx membrane, with near ballistic phonon transport along lithographically patterned legs [41] (Figure 2). RF power would be brought onto each TES using a thin-film superconducting microstrip transmission line, which runs along one of the supporting legs, and then deposited in a tiny AuCu load on the membrane.…”