Monolithic fabrication of optical benches and scanning mirror using silicon bulk micromachining

Abstract

This paper details an optical scanning mirror with a 54.74 inclined reflective plane and optical benches to align the optical components simply in a monolithic silicon substrate so as to implement a miniaturized laser scanner. The scanning mirror was designed and fabricated to achieve laser scanning on a miniaturized scale so that fluorescence detection of arrays of patterns on biochips can be performed by a handheld system. The inclined (111) reflective plane of the scanning mirror was formed by the KOH wet etching process, and proved to be a very appropriate structure for the assembly of optical scanning systems composed of a laser input and a scanning mirror in a silicon substrate. The optical benches, torsion spring and comb electrodes were fabricated using the DRIE process. The scanning mirror is actuated by its moment of inertia, the electrostatic torque of the comb electrodes and the restoring torque of the torsion spring. As designed, the scanning mirror is 2165 x 778 mu m 2 in an upper part of the rotor of the mirror, and the chip size including optical bench guides is 9 x 10 x 1 mm(3). The deflection angle of the scanning mirror was measured by a laser displacement meter (LC2420, Keyence, Japan), and the optical components were assembled and aligned in optical bench guides to observe the laser scanning. The deflection angle of the scanning mirror depends on matching the frequency of the driving signal and the mechanical oscillation of the scanning mirror, and a maximum deflection angle of 7 was obtained when a 16 V peak-peak square wave was applied to the comb electrodes. The scanning mirror with an inclined reflective plane and optical benches fabricated in a monolithic silicon substrate was proved to be a smart structure to implement a handheld-type scanning system for biochip application.