Evaluation of prototype 100 mK bolometric detector for Planck Surveyor

The High-Frequency Instrument (HFI) for the Planck Surveyor mission will me asure anisotropies of the Cosmic Microwave Background (CMB) down to scales of 6 arcmin and to an accuracy of Delta T/T = 2 x 10(-6). Channels ranging in frequency from 100 to 857 GHz will use 100 mK spider web bolometer detec tors with NTD Ge thermistors, The detectors must be photon noise limited an d fast enough to preserve signal information at the 1 r.p.m. scan rate of t he satellite. The prime low-frequency CMB channels at 143 and 217 GHz are t he most technically demanding owing to the lower background limited NEPs. F or the 143 GHz channel the requirements are that the time constant tau < 5. 7 ms and The NEPbol <1.53 x 10(-17) WHz(-1/2) including contribution from a mplifier noise. We present here thermal, electrical and optical data on a p rototype detector which, although optimised for the 100 GHz channel, satisf ies most of the requirements of the more demanding 143 GHz channel. The mea surements art: consistent with ideal thermal behaviour of the detector over the appropriate bias and temperature ranges for optimum performance. From optically blanked electrical measurements we determined the dependence of r esistance and thermal conductance on temperature over a wide range, 70-200 mK. The optical responsivity and NEP were measured under photon background conditions similar to those expected in flight. Measurements of speed of re sponse as a function of bias at different temperatures allowed us to determ ine the variation of total heat capacity with temperature. Extrapolation of these data show that in principal performance for all the Planck HFI chann els can be met, (C) 2000 Elsevier Science B.V. All rights reserved.