Automated micro-assembly of surface MEMS mirrors by centrifugal force

Abstract

A very fast, low-cost, and reliable method to assemble micro structures suitable for MOEMS (micro-opto-electro-mechanical systems) applications is reported in this paper. In general, due to the minute scale of MEMS devices, inertia force is often neglected when dealing with MEMS components. However, we have demonstrated that inertia force can be significant even if the mass of micro structure is <lpg (a 250pxlOOpn mass with 3 . 5~ thick polysilicon and 0 . 5~ thick Au layers). At this scale, we have shown that, mass inertia force can overcome some surface forces and thus be used for non-contact self-assembly of MEMS structures. Centrifugal force was applied to MUMPS (Multi-User-MEMS-Processes) chips by attaching the chips to a retathg disc. The micro hinged structures OR the chips were shown to self-assemble by rotating themselves 90' out of substrate plane in most cases, and automatically lock themselves to designed latches. The assembly process is also applicable to complex dynamic micro mirror structures. Our experimental setup and systematic approach to acquire force data during the centrifugal assembly process is described in this paper.

Force Sensing and Control in Micromanipulation

“…Another example of using inertial effect to deal with adhesion forces was reported by Lai et al [28]. In a microassembly task, a cantilever-like plate is to be lifted up to assemble the entire structure constrained by hinges, as illustrated in Fig.…”

“…In an ambient manipulation environment, it is impossible to change gravitational force. However, inertial force can be easily amplified by, for instance, generating an instantaneous acceleration [27], or increasing centripetal acceleration [28]. If inertial force can be made one order of magnitude greater than adhesion forces, then the effect of adhesion forces will become inconsequential.…”

“…Although the released pollen flied randomly after acceleration, it was constrained in a container for collection. In the application of noncontact assembly by centrifugal force [28], micromirrors also automatically locked themselves to designed latches after spinning.…”

Novel automated microassembly mechanism based on on-chip actuators

“…cos α þ f sin αÞp n cos β: (10) Furthermore, f ¼ μF and the static friction coefficient 34 μ is 0.4.…”

“…Various automated microassembly mechanisms have been developed which include (1) centrifugal force, 9,10 (2) magnetic force, 11 (3) external electrostatic force, 12,13 (4) themokinectic, 14 (5) residual stress, 15,16 (6) liquid flow and chemical, [17][18][19] (7) template, 20 and (8) on-chip microactuator-based [21][22][23][24] assembly technologies. Among those automated microassembly technologies, the on-chip microactuator assembly is very promising for several reasons.…”