Frequency Selective Cold-Electron Bolometer Arrays

Abstract: This work presents the integration of the Cold-Electron Bolometer (CEB) in Frequency Selective Surface (FSS) based arrays targeting balloon-borne telescope missions with high incident power requirements (typically tens of pW). FSS are planar frequency sensitive structures typically consisting of repeating pattern of a simple motif like square, circle, etc. This creates an array structure that is impedance matched to incident electromagnetic radiation. We investigated the integration of CEB detectors in these arrays and their response to incident millimeter/submillimeter radiation. The inherent frequency sensitive characteristics of the FSS allow these kinds of arrays to be designed for a wide range of frequency bands with coupling efficiencies approaching unity. A prototype 23 pixel CEB array at 345 GHz was developed for the OLIMPO telescope for performing photometric and spectroscopic observations of the Sunyaev– Zel'dovich effect from clusters of galaxies. Measurements from test pixel indicate a responsivity up to 2x10^8 V/W at low background powers. Spectral measurements indicate a bandwidth of about 20 GHz. Using room temperature commercial amplifiers, the Noise Equivalent Power (NEP) was estimated as 2x10^-16 W\sqrt{Hz} ,which is larger than the theoretically modelled value by a factor of 4-5. Prototype pixels which could possibly be used for the 145 GHz and 95 GHz channels on the SWIPE instrument in the LSPE balloon-borne telescope have also been developed and characterised. The spectral response of the 95 GHz pixels closely matches RF simulations with a bandwidth of about 8 GHz. An efficiency greater than 70% is estimated from analysis of measured data with responsivity approaching 1x10^{8} V/W at a background power of 60 pW.