Fabrication of a tetrahedron folding pattern, extra steps.

(a): Since only one of the hinges lies on the correct intersection of the planes, standard lithography is used to define flat hinges for the other faces. Faces 2 and 3 are designed with small appendices on their sides to allow them to lock onto face 1 while folding. (b): Under-etching of Si by semi-isotropic etching of silicon (SF₆ etchant). Etching is stopped when the hinges are free and the central flap rests on a silicon pillar.