Modelling of Microspring Thermal Actuator

Abstract The deflection of a chevron actuator strongly depends on the length and the angle of the beams; a larger deflection is produced if a smaller angle is used. The drawback is that it is a single beam like device. To deliver a larger displacement, even longer beams are required for chevron actuators. This is problematical in term of fabrication and operation, as the long beams easily buckle or stick to the substrate. Therefore the beam length of a chevron device is limited, typically to a 200Pm long, which in-turn limits the amount of the displacement and applications. In our new type of device, instead of using a single long beam, the arm is folded into a number of chevron sections to become a planar spring-like actuator as shown in Fig.1.b. (2 chevrons with 1 linkage bar are defined as 1 ring). An insulating beam with a very low thermal expansion coefficient is used to form a cross-linkage thereby constraining the displacement in the x-direction. As the actuator is heated up under bias, the thermal expansion of the active material leads to a displacement in the y-direction only. A new type of Microspring (P-spring) electrothermal actuator consisting of multi-chevron structures was proposed. Finite element analysis was used to model the device performance, and the results compared with that of chevron thermal actuator. The simulation showed that the P-spring actuator can deliver a much large deflection than that of chevron actuator. The deflection is proportional to the number of chevron structures linked together. By linking more chevron structures, this P-spring can deliver a larger displacement than any other thermal actuators. The device has a much smaller footage than that of a single chevron device for a similar amount of deflection. Electroplated Ni thin film and SiO2 were used as active and linkage materials to fabricate the P-spring actuator