Cryogenic etching of silicon, using an inductively coupled plasma reactive ion etcher (ICP-RIE), has extraordinary properties which can lead to unique structures difficult to achieve using other etching methods. In this work, the authors demonstrate the application of ICP-RIE techniques which capitalize on the cryogenic properties to create different sensors geometries: optical, electrical, magnetic, and mechanical. The three techniques demonstrated are (1) single step deep etches with controllable sidewall profiles. Demonstrating this, silicon pillars with over 70 mu m depth and less than 250 nm sidewall roughness were etched using only 1.6 mu m of photoresist for use as solar cells. (2) Using the cryogenic etch for thick metallization and liftoff with a thin photoresist mask. Demonstrating this second technique, a magnetic shim was created by deposition of 6.5 mu m of iron into 20 mu m deep etched trenches, using the remaining 1.5 mu m photoresist etch mask as the liftoff mask. Using the same technique, 15 mu m of copper was lifted off leaving a 20 mu m deep plasma enhanced chemical vapor deposition silicon oxide coated, silicon channel with copper. (3) Use of a two step cryogenic etch for deep etching with reduced sidewall undercutting. This was demonstrated by fabrication of deep and anisotropic microelectromechanical systems structures; a mechanical resonator was etched 183 mu m deep into silicon with less than 3 mu m of undercutting. This work also describes the etch parameters and etch controls for each of these sensors.