Wafer-level mechanical and electrical integration of SMA wires to silicon MEMS using electroplating

Abstract

This paper reports on the wafer-level fixation and electrical connection of pre-strained SMA wires on silicon MEMS using electroplating, providing high bond strength and electrical connections in one processing step.The integration method is based on standard micromachining techniques, and it potentially allows mass production of microactuators having high work density.SEM observation showed an intimate interconnection between the SMA wire and the silicon substrate, and destructive testing performed with a shear tester showed a bond strength exceeding 1 N.The first Joule-heated SMA wire actuators on silicon were fabricated and their performance evaluated. Measurements on a 4.5 x 1.8 mm 2 footprint device show a 460 µm stroke at low power consumption (70 mW).

Wafer-level integration of NiTi shape memory alloy wires for the fabrication of microactuators using standard wire bonding technology

“…This is an important measure for the design of the chip-level fixation of the SMA wire, which could e.g. be performed with Ni-electroplating in a subsequent step [9]. In addition, a basic evaluation of the mechanical robustness of the anchor and clamp structures was performed by implementing a simple actuator.…”

A low-power high-flow shape memory alloy wire gas microvalve

“…The lowest of the actuator deflection and orifice height therefore determines the open-state flow. For 3 mm long cantilever arms, a deflection of over 450 μm can be achieved [17], while the current orifice height is 200 μm. By increasing the height of the orifice channel to match the actuator deflection, the open-state flow can be doubled.…”

“…When the current to the SMA is removed, the wires cool and the cantilevers stretch the SMA wires again, thus closing the gate ( figure 3(a)). The actuator retains a residual deflection in the cold state [17].…”

“…Thereafter, a second Bosch DRIE is performed from the top side to form the silicon cantilevers, the gate and the gap between the gate and the flow orifice ( figure 6(a)) [16]. Prestrained NiTi SMA wires (Dynalloy Flexinol HT, with a nominal A f transformation temperature of 90 • C) are then transferred onto the silicon wafer ( figure 6(b)) and both mechanical and electrical connections are formed by Ni-electroplating ( figure 6(c)), as presented in [17]. Finally, the wafer is diced into individual chips.…”

“…Very promising integration processes of NiTi wires on silicon for the creation of robust actuators have been reported using adhesive bonding [16], electroplating [17] and wire bonding [18]. The initial material cost for SMA wires is very low, since commercially available actuator materials are used.…”