Compact Low-Voltage Operation Micromirror Based on High-Vacuum Seal Technology Using Metal Can

Abstract

In this paper, we present the design, fabrication, and vacuum package of an electrostatic comb-drive resonant micromirror. The micromirror having a high resonant frequency suitable for a laser scanning display was fabricated using a silicon-on-insulator (SOI) wafer. An individual die which was an array of four micromirrors with a total size of 5.5 × 5.5 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> was diced from the SOI wafer by dry etching. The die was packaged in a transistor-outline-8 metal can with a window in a vacuum-packaging machine at a pressure of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> Pa. To evacuate the residual gases generated after the package process, a nonevaporable getter was used in the metal can. The resonant frequencies of the fabricated micromirrors were 13 and 25 kHz, respectively. An optical rotation angle of about 10° was achieved at a low driving voltage of 5 V. Due to the decrease of air-friction loss, the operation voltage decreased by a factor of 32 compared with the voltage operated at atmospheric pressure. The operation pressure in the vacuum package was evaluated to be about 0.7 Pa from the amplitude and quality factor of the mirror oscillation. Moreover, several properties, such as the surface profile of the micromirror, were evaluated before and after the packaging. The durability of the packaged mirror was tested at temperatures of up to 75°C. The theoretical explanations about air friction were also described.