Applied Physics

Building Suspension Bridges

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Science  08 Jun 2001:
Vol. 292, Issue 5523, pp. 1801
DOI: 10.1126/science.292.5523.1801a

The successful development of microelectromechanical (MEM) systems will depend on robust techniques for forming mechanical structures readily and reproducibly on the micrometer scale. Strittmatter et al. demonstrate the ability to form suspended membranes of p-type GaN, a material whose large piezoelectric response and chemical resilience make it an ideal candidate for MEM applications, especially in harsh environments. The p-type GaN is deposited on a sacrificial layer of n-type GaN. When placed in aqueous potassium hydroxide and exposed to ultraviolet illumination, the n-type material becomes photosensitive and etches away, leaving a freestanding p-type layer. Regions of n-GaN shielded from illumination by patterned metal photomasks deposited on the p-GaN act as pillars to hold the bridge in place. Application of a small positive bias to the metal mask regions during the electrochemical etch results in an enhanced etch rate approaching 30 micrometers per minute. — ISO

Appl. Phys. Lett. 78, 3226 (2001).

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