Properties of metal bolometers fabricated on porous silicon

Recent studies on thermal properties of porous silicon (PS) made possible a new type of structures and processes for a better thermal insulation of ch emical and physical sensors. In this work, we propose to use PS as substrat e for the sensing element of metal bolometers. PS is obtained by electroche mical anodization of bulk Si in HF-based solutions. By varying HF title and current density during anodization, well defined thin layers with differen t porosities can be obtained. The sensing elements of the bolometer is a Nb strip, 5 mu m wide and 50 nm thick, deposited on PS 40 mu m thick. The the rmal properties of the strips on PS have been measured both by resistive he ating and bolometric method. The results have been compared with those obta ined on amorphous glass. Strips on a layer of PS 40 mu m thick with a poros ity of 60% show a thermal conductance close to that obtained on glass. A re sponsivity of about 50 V W-1 and a time constant of 4 ms have been measured for a bolometer deposited on PS with porosity of 60%. (C) 1999 Elsevier Sc ience B.V. All rights reserved.