Distributed TES Model for Designing Low Noise Bolometers Approaching SAFARI Instrument Requirements

P Khosropanah,L Gottardi,J R Gao,P A J De Korte,M A Lindeman,M Ridder,M Bruijn,R A Hijmering,H Hoevers,J Van Der Kuur

doi:10.1007/s10909-012-0550-6

Abstract

Transition edge sensors (TES) are the chosen detector technology for the SAFARI imaging spectrometer on the SPICA telescope. The TES are required to have an NEP of 2–3 × 10?19 W/? Hz to take full advantage of the cooled mirror. SRON has developed TiAu TES bolometers for the short wavelength band (30–60 ?m). The TES are on SiN membranes, in which long and narrow legs act as thermal links between the TES and the bath. We present a distributed model that accounts for the heat conductance and the heat capacity in the long legs that provides a guideline for designing low noise detectors. We report our latest results that include a measured dark NEP of 4.2×10?19 W/? Hz and a saturation power of about 10 fW.

Highlights

SPICA [1] is a Japanese-led mission to fly a 3.25 m diameter IR telescope with a cryogenically cooled mirror (∼5 K)
We present a distributed model that accounts for the heat conductance and the heat capacity in the long legs that provides a guideline for designing dark NEP
Cooling the optics reduces the background radiation caused by the ambient temperature of the FIR space telescopes that limits the sensitivity

Summary

Introduction

J.R. Gao Kavli Institute of NanoScience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands. Is required for detectors on a ground based telescope and impose a great challenge on the detector technology. Transition edge sensor (TES) is the chosen detector for the SAFARI instrument. In collaboration with several European institutes, SRON is developing low thermal conductance TES bolometers that are based on Ti/Au bilayer as the sensitive element on suspended silicon nitride (SiN) membranes. The measured dark NEPs in our original devices were typically a factor of 2–3 higher than what were expected from the measured thermal conductance [3]. We argue that part of the excess noise is due to the thermal fluctuation in the supporting legs and present a distributed leg model that provides a guideline for designing low noise devices. We support the model by our latest measurement results

Distributed Model

Low Noise Design Guidline