a large-displacement electromagnetic mems actuation system … · a large-displacement...
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A Large-Displacement Electromagnetic MEMS Actuation System
Matt Neal, Alan L. Sidman, Justin Borski Advanced Microsensors
333 South Street, Shrewsbury, MA 01545 [email protected]
A low-voltage, large-displacement MEMS magnetic actuator platform has been developed for a broad range of potential applications, including switches, relays, variable capacitors, resonators, micro-positioners, optical switches, attenuators, filters, gratings, fluidic pumps and valves, etc. The devices are robust as tested for temperature/humidity cycling, hot and cold storage, mechanical shock, and vibration. The design concept, finite-element magnetic and mechanical modeling, device build-up, materials and process development, and performance results for this actuator will be discussed.
Attributes of the platform design include deep reactive ion etched (DRIE) suspension and actuatable elements fabricated on a silicon-on-insulator (SOI) wafer (Fig.1), a micro-electromagnet consisting of an electrodeposited conductor fabricated as a three-dimensional winding around an electrodeposited soft magnetic core and separated from the core by planarizing polymer insulation (Fig. 2), a high remnant magnetization (200 memu/cm2) actuator, and anti-stiction features.
Finite element modeling of both the electromagnetic (Fig. 3) and mechanical (Fig. 4) systems has been used to optimize element design and dynamic performance. The device features low voltage (< 1V) operation for ease and reduced cost of integration into low voltage microelectronic and opto-electronic systems. No step-up transformer or charge pump is required as with electrostatically actuated devices. Larger strokes are easily attainable with this scalable platform. Actuation is bi-directional, depending on current sense. Response curve shape can be tailored with magnet design to suit the application (Fig. 5). The magnetic and mechanical systems are completely separable so that design adjustments can be made independently.
Processes developed and utilized include: epitaxial permanent magnet multi-layer sputter deposition, composite masking for DRIE, UV_LIGA micro-lithography, through-mask precision electrodeposition of low resistance 3D solenoidal conductors and soft magnetic alloy cores, low cure temperature planarizing polymer insulation, buried oxide release etch, and anti-stiction supercritical CO2 clean and dry.
Figure 1. Actuation and suspension elements deep-reactive-ion-etched (DRIE) to buried oxide layer of SOI wafer.
Figure 2. Three-dimensional micro-electromagnet with copper windings and Permalloy core.
Figure 3. Flux density map of electromagnetic actuation system derived from finite element analysis.
Figure 4. Displacement in the actuation direction of the mechanical system derived from finite element analysis.
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Figure 5. Electromagnetic MEMS response curve.