Electromechanical actuators that convert electrical energy into mechanical force or motion are an integral part of any electrically powered system with moving parts. Examples of such systems with subcentimeter dimensions include microrobots1,2,3,4, precision positioning systems5,6,7,8, optical systems9,10,11 and medical devices12,13,14,15,16. For such applications, the actuator must provide displacements ranging from tens of micrometers to millimeters and supply forces in the mN range. Batch-fabricated micromachined (Microelectromechanical system) actuators can provide low-cost highly integrated solutions for these applications. However, none of the existing micromachined electrostatic actuators can meet the large energy output requirements. Transduction mechanisms commonly used in micromachined actuators include electrostatic, piezoelectric, electrothermal, and electromagnetic mechanisms. Electromagnetic transduction, which is the main means of electromechanical energy conversion in macroscale systems, has been conventionally used in smaller scale systems. These actuators, such as voice coil motors (VCM), can produce relatively large force and displacement and are widely used for autofocus (AF) and optical image stabilization (OIS) in compact camera modules in modern consumer electronics (smartphones, tablets, etc.)17,18,19. However, the need for high-turn coils and magnets makes such actuators difficult to miniaturize and batch fabricate by micromachining. They are also not power efficient due to the need for significant current flow in the coils, potentially even when the actuator is not moving. Piezoelectric actuators, on the other hand, are very power efficient and provide a high output force, but a very small stroke necessitates aggressive leverage mechanisms to reach adequate displacements at the cost of lowering the force20,21,22. Furthermore, since the inclusion of piezoelectric materials in micromachining processes is mainly limited to thin films, reaching a large overall actuator active layer size and thus a high energy output is very challenging. Finally, electrothermal microactuators utilizing thermal expansion and contraction of heated elements can produce large force and displacement (with leverage), but their high-power consumption is prohibitive for most applications23,24.
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