Fabrication of silicon bolometers with bulk micromachining technology

Monolithic silicon bolometers with implanted thermistors, micromachined thermal masses and suspension beams have been developed. These devices are intended for accurate β-decay spectrum measurements in the Milano neutrino mass experiment. By means of a dedicated micromachining fabrication process very small thermal masses (700×430×15 μm3) and links (2150×22×15 μm3) have been directly integrated in the device, thus obtaining reproducible bolometers which are suitable for use in detector arrays. The fabrication process involves a combination of standard IC technologies and bulk micromachining techniques, based on wet etching steps in tetramethylammonium hydroxide (TMAH) water solutions. Protection of aluminum metal lines and surface roughness control are two important features of the developed technique. The proposed micromachining approach eventually aims at fabricating hundreds of highly reproducible bolometers, to be used simultaneously in order to improve the sensitivity of the neutrino mass experiment.