Methods for forming and releasing microelectromechanical structures

A method for making a micromirror array for a projection display, comprising:

• depositing a sacrificial material on a substrate;
• forming an array of micromirrors comprised of mirror plates and hinges, wherein the hinges of the micromirrors comprise an early transition metal (groups 3-7 of the periodic table) nitride;
• and
• releasing the micromirrors by removing the sacrificial material in a spontaneous gas phase chemical etchant selected from interhalogens and noble gas halides, wherein the early transition metal nitride is exposed to the etchant during removal of the sacrificial material but remains after the micromirrors are released.

A method of making a micromirror array device, the method comprising:

• deposition a sacrificial material on a substrate;
• forming an array of micromirrors comprised of mirror plates and hinges, wherein the hinges comprise TiNx;
• and
• releasing the micromirrors by removing the sacrificial material in a spontaneous gas phase etchant comprising gas phase xenon difluoride, wherein the TiNx is exposed to the etchant during removal of the sacrificial material but remains after the micromirrors being released.