Development of Ultra-Low-Noise TES Bolometer Arrays

• DOI: 10.1007/s10909-015-1401-z
• Publication Date: 2015-12-29T10:03:19Z
• Authors: T. Suzuki; P. Khosropanah; M. L. Ridder; R. A. Hijmering; J. R. Gao; H. Akamatsu; L. Gottardi; J. van der Kuur; B. D. Jackson
• Keywords: 0103 physical sciences; 01 natural sciences

SRON is developing ultra-low-noise transition edge sensors (TESs) based on a superconducting Ti/Au bilayer on a suspended SiN island with SiN legs for SAFARI aboard SPICA. We have two major concerns about realizing TESs with an ultra-low NEP of $$2\times 10^{-19}~\hbox {W}/\sqrt{{\text {Hz}}}$$ : achieving lower thermal conductance and no excess noise with respect to the phonon noise. To realize TESs with phonon-noise-limited NEPs, we need to make thinner ( $${<}0.25~\upmu \hbox {m}$$ ) and narrower ( $${<}1~\upmu \hbox {m}$$ ) SiN legs. With deep reactive-ion etching, three types of TESs were fabricated in combination with different SiN island sizes and the presence or absence of an optical absorber. Those TESs have a thin $$(0.20~\upmu \hbox {m}$$ ), narrow (0.5–0.7 $$\upmu \hbox {m}$$ ), and long (340–460 $$\upmu \hbox {m}$$ ) SiN legs and show $$T_{\mathrm {c}}$$ of $${\sim }93~\hbox {mK}$$ and $$R_{\mathrm {n}}$$ of $${\sim }158~\hbox {m}{\Omega }$$ . These TESs were characterized under AC bias using our frequency-division multiplexing readout (1–3 MHz) system. TESs without the absorber show NEPs as low as $$1.1\,\times \,10^{-19}~\hbox {W}/\sqrt{{\text {Hz}}}$$ with a reasonable response speed ( $${<}1~\hbox {ms}$$ ), which achieved the phonon noise limit. For TESs with the absorber, we confirmed a higher $$\hbox {NEP}_{\mathrm {el}} ({\sim }5\,\times \,10^{-19}~\hbox {W}/\sqrt{{\text {Hz}}}$$ ) than that of TESs without the absorber likely due to stray light. The lowest NEP can make the new version of SAFARI with a grating spectrometer feasible.