Abstract
A high-aspect-ratio three-dimensionally (3D) stacked comb structure for micromirror application is demonstrated by wafer bonding technology in CMOS-compatible processes in this work. A vertically stacked comb structure is designed to circumvent any misalignment issues that could arise from multiple wafer bonding. These out-of-plane comb drives are used for the bias actuation to achieve a larger tilt angle for micromirrors. The high-aspect-ratio mechanical structure is realized by the deep reactive ion etching of silicon, and the notching effect in silicon-on-insulator (SOI) wafers is minimized. The low-temperature bonding of two patterned wafers is achieved with fusion bonding, and a high bond strength up to 2.5 J/m2 is obtained, which sustains subsequent processing steps. Furthermore, the dependency of resonant frequency on device dimensions is studied systematically, which provides useful guidelines for future design and application. A finalized device fabricated here was also tested to have a resonant frequency of 17.57 kHz and a tilt angle of 70° under an AC bias voltage of 2 V.
Highlights
The term “plenty of room at the bottom” [1] is synonymous with the birth of the complementary metal–oxide–semiconductor (CMOS), with exponential growth in the last six decades for the semiconductor industry
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This is in agreement with Equation (3) given earlier, where the Wm increases the torsional moment of inertia, Iθ, subsequently reducing the resonant frequency f 0 in Equation (1)
Summary
The term “plenty of room at the bottom” [1] is synonymous with the birth of the complementary metal–oxide–semiconductor (CMOS), with exponential growth in the last six decades for the semiconductor industry. This work presented here combines the design and demonstration of a high-aspectratio 3D MEMS vertical comb structure, where a novel low-temperature bonding process of two patterned wafers is achieved for the first time. This is a key processing method to realize the 3D vertical comb structures. In order to generate a high electrostatic torque with a large tilt angle, vertical comb drives with a high-aspect-ratio profile (>40 μm deep, 6um width fingers) have been fabricated by DRIE technology. With total freedom in three dimensions with these stacking structures, the devices are expected to achieve a higher tilt angle than the conventional 2D planar devices
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