Magnetic field assisted bonding technology for released micro actuator and mirror surface

Abstract

A magnetic field pulling-force assisted bonding technology is reported, which is used to bond a mirror plate with a released microactuator using adhesive. This bonding technology is not sensitive to the micromachining process, i.e., any process for microactuator fabrication containing the ferromagnetic structure layer can be used and bonded with a high surface quality mirror plate after released. The conventional wafer bonding technology bonds unreleased actuator with a mirror plate but it limits to the process compatible with the wafer bonding with a releasing step suitable for wafer bonding. Consequently not all processes (such as those mature and commercially available, and those being able to generate large displacement) can be used to fabricate micromirrors. The bonding technology proposed in this paper applies non-touching magnetic field pulling-force, instead of conventional compression mechanical force through touching, to bring the microactutor and a mirror plate in contact for bonding such as to avoid: (1) any plastic deformation or damage to the released micro actuator; and (2) the risk of sticking the actuator moving part to the substrate due to the adhesive squeezed out from the bonding surfaces. The bonding method is introduced and the critical parameters of the bonding method, i.e., distance between the magnet to the actuator is determined through simulations. A bonding mechanism is built and two different designs are bonded. Bonding results are measured, which verifies the bonding method. The bonding is characterized to have a strength of withstanding vibration for a few hours in frequency 20–200 Hz with 2–5 g acceleration and surviving in the temperature of −30 to 80 °C. After bonding a mirror plate with 15.6 m of the curvature radius and 2 nm of the roughness, the bonded micromirror is tested to have a quasi-static displacement of 120 μm.