Transition edge sensor (TES) is the selected detector for the SAFARI FIR imaging spectrometer (focal plane arrays covering a wavelength range from 30 to 210 μm) on the Japanese SPICA telescope. Since the telescope is cooled to <7 K, the instrument sensitivity is limited by the detector noise. Therefore among all the requirements, a crucial one is the sensitivity, which should reach an NEP (Noise Equivalent Power) as low as 3E-19 W/Hz^0.5 for a base temperature of >50 mK. Also the time constant should be below 8 ms. We fabricated and characterized low thermal conductance transition edge sensors (TES) for SAFARI instrument on SPICA. The device is based on a superconducting Ti/Au bilayer deposited on suspended SiN membrane. The critical temperature of the device is 155 mK. The low thermal conductance is realized by using narrow SiN ring-like supporting structures. All measurements were performed having the device in a light-tight box, which to a great extent eliminates the loading of the background radiation. We measured the current-voltage (IV) characteristics of the device in different bath temperatures and determine the thermal conductance (G) to be equal to 1.66 pW/K. This value corresponds to a noise equivalent power (NEP) of 1E-18 W/√Hz. The current noise and complex impedance is also measured at different bias points at 25 mK bath temperature. The measured electrical (dark) NEP is 2E-18 W/√Hz, which is about a factor of 2 higher than what we expect from the thermal conductance that comes out of the IV curves. Despite using a light-tight box, the photon noise might still be the source of this excess noise. We also measured the complex impedance of the same device at several bias points. Fitting a simple first order thermal-electrical model to the measured data, we find an effective time constant of about 65 μs and a thermal capacity of 3-4 fJ/K in the middle of the transition
[1]
K. Souccar,et al.
The AzTEC mm-wavelength camera
,
2008,
0801.2783.
[2]
V. V. Hristov,et al.
The BOOMERANG North America Instrument: A Balloon-borne Bolometric Radiometer Optimized for Measurements of Cosmic Background Radiation Anisotropies from 0.°3 to 4°
,
2001,
astro-ph/0105148.
[3]
J. J. Bock,et al.
Measurements of Sunyaev-Zel’dovich Effect Scaling Relations for Clusters of Galaxies
,
2004,
astro-ph/0404391.
[4]
J. Bock,et al.
Silicon nitride Micromesh Bolometer Array for Submillimeter Astrophysics.
,
2001,
Applied optics.
[5]
Bruce M. Swinyard,et al.
ESI: the far-infrared instrument for the SPICA mission
,
2006,
SPIE Astronomical Telescopes + Instrumentation.
[6]
S Masi,et al.
Instrument, Method, Brightness and Polarization Maps from the 2003 flight of BOOMERanG
,
2005,
astro-ph/0507509.