Magnetic Microactuation of Polysilicon Flexure Structures

— A microactuator technology that combines magnetic thin films with polysilicon flexural structures is described. Devices are constructed in a batch-fabrication process that combines electroplating with conventional lithography, materials, and equipment. A microactuator consisting of a 400x(47-40)x7 µm 3 rectangular plate of NiFe attached to a 400x(0.9-1.4)x2.25 µm 3 polysilicon cantilever beam has been displaced over 1.2 mm, rotated over 180°, and actuated with over 0.185 nNm of torque. The microactuator is capable of motion both in and out of the wafer plane and has been operated in a conductive fluid environment. Theoretical expressions for the displacement and torque are developed and compared to experimental results. I. INTRODUCTION AGNETIC microactuation has recently been demonstrated by several research groups [1-6]. In most cases magnetic-microactuator fabrication is not accomplished in a continuous batch process, but rather with the addition of steps such as manual assembly. The cantilever actuator described by Ahn and Allen is an exception [3]. We describe here batch-fabricated magnetic microactua-tors which are made in a relatively simple process [7]. This process combines electroplated NiFe films with surface -micromachined polycrystalline silicon, a combination of materials that provides new opportunities for actuated-structure designs. In addition, forces and displacements that are larger than those generated by most electrostatic microactuators are readily obtained. An important feature of this technology is provided by the ability to control actuation via a remote source for the magnetic field. This type of control can conveniently actuate structures both in and out of the plane of the wafer. These advantages of magnetic drive can accelerate and broaden the already impressive results obtained with actuated polysilicon microflexural elements [8-10]. Liu et. al have recently applied similar technology to arrays of actuators for flow-stream control on aircraft wing surfaces [11]. Integration of magnetically actuated elements into microsystems will add new dimensions to MEMS. There appears to be no major obstacle to the merger of electrical , mechanical, and magnetic microfabrication technologies .