Design, Modeling, and Testing of High Performance RF Bistable Magnetic Actuators
Gray, Gary Dean, Jr.
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Due to the limitations of electrostatic RF actuators, magnetic actuation was investigated, and the optimal design space for a bistable magnetic actuator with ultra-low actuation energy and large actuation distance (100 m) has been modeled. Attention was paid to minimizing the energy expended to minimize heat dissipation and power consumption so that the device could be used over a wide temperature range, including cryogenic environments. A more desirable switching regime existing for low magnetic fields (10 mT) was found that requires shorter pulses (s vs ms) and lower actuation energy (less than 5 J vs 100 J) than designs outside of this space. The device was modeled to latch in two states, based on the interaction of the magnetic actuator with an external magnetic field. Based on this model, a bistable magnetic MEMS actuator was fabricated using microelectronic processes including a two-substrate flip-chip assembly, multilevel metallization, and sublimation release to avoid stiction. The actuator was found to have excellent correspondence between observed and modeled behavior. The benefits of shape anisotropy are quantified. Lithographic patterning of the magnetic material into long narrow strips along the actuators length resulted in much greater magnetic torques being developed at reduced external field levels. Low levels of anisotropy led to designs with low levels of magnetization and therefore required higher external magnetic fields, whereas high levels of anisotropy led to designs latching at 10 mT levels with contact forces greater than 5 N with switching energies less than 100 J and a switching speed of less than 5 ms. More moderate levels of anisotropy resulted in a design space where less than 1 J switching energies could be realized. Electrical performance has been demonstrated over 2 million cycles, and mechanical performance to 150 million cycles. Applications include electronics, microfluidics, and cryogenic devices.