A bistable snapping microactuator

A mechanical bistable switching device, actuated by the interactive forces of a buckling cantilever and a tension band connected to its end, is described. The device has been built using a combination of surface- and bulk-micromachining on materials familiar in IC fabrication: a silicon substrate, LPCVD layers of polycrystalline silicon (polysilicon), silicon nitride, and silicon dioxide. The switching element is a cantilever formed from three thin-film layers: polysilicon, silicon dioxide, and polysilicon. The cantilever is made to buckle as a result of strong axial force from a built-in tension band. Joule heating in one of the two polysilicon layers of the buckled cantilever gives rise to a snapping action that moves the cantilever end ±6 μm in a direction perpendicular to the underlying silicon substrate. The overall device length, excluding contact pads, is less than 200 μm; it has an 82 μm-long buckling cantilever, a 70 μm-long silicon nitride tension band, and a 105 μm-long extra cantilever, called a tension-band anchor The substrate under the device is recessed to accommodate large vertical movement of the actuator. The device is operated by heating the cantilever asymmetrically with a current of 7 mA at 24 V for 12 μsec, after uniform heating of the tension-band anchor with another current pulse of 3 mA at 7.5 V for 50 msec. The fabrication process used to make the device is briefly reported