Microstructures and single mask, single-crystal process for fabrication thereof

A single-mask, low temperature process for fabricating high aspect ratio released microelectromechanical structures comprising:

• forming mask dielectric mask layer on a substantially horizontal top surface of an etchable substrate;
• patterning producing in said mask layer to produce a single dielectric mask pattern defining a structure of arbitrary shape to be formed in said substate and including at least a of crystal orientation in said substrate and including at least a beam portion to be released for movement with respect to said substrates;
• etching said substrate through said dielectric mask pattern to produce a corresponding continuous trench having substantially vertical side walls and a substantially horizontal floor in said substrate to thereby produce said structure of arbitrary shape in said substrate, said structure being completely surrounded by said trench, having a top surface covered by said mask layer, and having vertical side walls produced by said trench, and said substrate having vertical side walls spaced from said structure by said trench;
• forming a second dielectric layer on said walls, on the floor of said trench, and on said dielectric mask layer;
• removing said second dielectric layer from the dielectric mask layer and from the floor of said trench to expose the substrate at said floor while leaving said dielectric mask layer and said side wall dielectric layers substantially intact;
• releasing at least said beam portion of said structure by etching said exposed substrate at the floor of said trench, the etching completely undercutting said beam portion to free it for motion with respect to said substrate and partially undercutting said structure and said substrate side walls;
• and
• thereafter coating said structure and said substrate with a metal an electrically conductive layer, the metal conductive layer on said structure being electrically isolated from the metal conductive layer on the substrate by said trench and by said undercutting of said structure and said substrate side walls.