Fabrication of a microelectromechanical system mirror array and its drive electrodes for low electrical interference in wavelength‐selective switches

Abstract

This article describes the fabrication of a microelectromechanical system (MEMS) mirror array and mirror‐drive electrodes with high‐aspect‐ratio gold walls that reduce electrical interference in a wavelength‐selective switch (WSS). The MEMS mirror array, in which a lot of closely spaced adjacent mirrors are electrostatically operated, can be fabricated with a high yield by encapsulating the mirrors with an organic film that protects them from process damage. The gold walls with a high‐aspect ratio are formed in the narrow space between adjacent mirror‐drive electrodes by using thick‐multilevel interconnection technology. Because of these walls between adjacent electrodes, each MEMS mirror operates with low electrical interference. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Deformation and Restoration of Shape in Microelectromechanical System Membrane

“…11,12 However, the process often causes the z E-mail: sakata.tomomi@lab.ntt.co.jp oxidization of the Si membrane surface, which results in unexpected movement of the membrane due to the charge accumulated in the oxidized surface. Therefore, the oxidized surface has to be removed to prevent such charge drift.…”

“…XPS -before and after Ar plasma exposure.-In MEMS device fabrication, oxygen plasma exposure is usually used to ash off an organic sacrificial layer. 11,12 However, the process often causes the z E-mail: sakata.tomomi@lab.ntt.co.jp oxidization of the Si membrane surface, which results in unexpected movement of the membrane due to the charge accumulated in the oxidized surface. Therefore, the oxidized surface has to be removed to prevent such charge drift.…”

Removal of Gold Oxide by Low-Temperature Hydrogen Annealing for Microelectromechanical System Device Fabrication

“…This means that vacuum annealing restores the oxidized surface to its initial gold state, just as HCl(aq) dipping does. [10][11][12]…”

“…[2][3][4][5][6][7][8][9] In such electroplating, there are incubation periods during which the gold oxide formed by the exposure to reactive oxygen disappears, and different incubation periods at different places give rise to nonuniform film thickness. [10][11][12] This is because oxidation easily occurs when a gold surface is exposed in highly reactive chemical environments, such as exposure to oxygen plasma or a combination of ultraviolet light and ozone (UV/ozone). [13][14][15][16][17] Therefore, the removal of the gold oxide is the key to fabricating uniform multilevel gold structures.…”

“…One way to remove the oxide is to dip the gold oxide surface in hydrochloric acid [HCl(aq)]. [10][11][12] However, this treatment is not necessarily applicable when there is a material on the surface that is soluble in HCl(aq), such as aluminum, or when there are very fragile microstructures on the surface that could be damaged by a wet process. Therefore, a dry process for gold oxide removal is desired.…”