Modelling and Fabrication of Microspring Thermal Actuator
J.K. Luo, A.J. Flewitt, M. Spearing, N.A. Fleck and W.I. Milne
University of Cambridge, UK
Keywords: spring electro-theraml, actuator, modelling
A new spring type microelectrothermal actuator with greatly enhanced displacement is proposed. Instead of using a single long chevron actuator, several chevrons are folded into a number of sections to become a spring-like actuator. Insulating beams with a very low thermal expansion coefficient are used to form cross-linkages thereby avoiding displacement in the x-direction. As the actuator is heated up under bias, thermal expansion of the material leads to displacement in the y-direction only. FEMLAB simulation shows that for each device, the displacement linearly increases with increasing arm length. By introducing folded arms, the device size is substantially decreased whilst still delivering a large displacement, which is proportional to the number of arms. Hence the displacement that can be achieved by thermal actuation is significantly increased. For instead, the displacement for chevron with l=400µm is ~17µm and the size of ~800_50µm. A spring actuator consists of four chevrons with l=100um, it delivers a 12.5µm displacement with a size of only ~220_100µm. As comparing with a single chevron actuator with l=100µm, the folded spring delivers almost 4 times the displacement. A 2-mask stages process is used to fabricate the device. A freestanding electroplated Ni spring arms without the cross-linkages has already been fabricated.
Nanotech 2004 Conference Technical Program Abstract