Planar Frequency Selective Bolometric Array at 350 GHz

Abstract

In this paper, we describe a bolometric focal plane array consisting of the cold electron bolometer (CEB) integrated in a frequency selective surface (FSS) fabricated on a silicon substrate with a backshort. This array is formed by a periodic pattern of conducting annular square and ring shapes and the two-terminal CEB is embedded directly in the element. The impedance of the CEB has been matched to the FSS which provides resonant interaction with incident sub-millimetre radiation. A further degree-of-freedom for the tuning is via varying the thickness of the substrate. We have been able to design the FSS at 350 GHz with peak coupling of more than 90% as is common for FSS based filters. A prototype of such a detector has been fabricated and optical response to blackbody radiation has been measured, indicating responsivities of $2\ast 10 ^{9}~{\hbox{V}}/{\hbox{W}}$ and higher at 185 mK and $3\ast 10 ^{8}~{\hbox{V}}/{\hbox{W}}$ and higher at 300 mK. The details of this new concept, together with numerical simulations and optical measurements are presented.