Bent-Beam Electrothermal Actuators--Part I: Single Beam and Cascaded Devices

This paper describes electrothermal microactuators that generate rectilinear displacements and forces by leveraging deformations caused by localized thermal stresses. In one manifestation, an electric current is passed through a V-shaped beam anchored at both ends, and thermal expansion caused by joule heating pushes the apex outward. Analytical and finite element models of device performance are presented along with measured results of devices fabricated using electroplated Ni and [p.sup.++] Si as structural materials. A maskless process extension for incorporating thermal and electrical isolation is described. Nickel devices with 410-[micro]m-long, 6-[micro]m-wide, and 3-[micro]m-thick beams demonstrate 10 [micro]m static displacements at 79 mW input power; silicon devices with 800-[micro]m-long, 13.9-[micro]m-wide, and 3.7-[micro]m-thick beams demonstrate 5 [micro]m displacement at 180 mW input power. Cascaded silicon devices using three beams of similar dimensions offer comparable displacement with 50-60% savings in power consumption. The peak output forces generated are estimated to be in the range from 1 to 10 mN for the single beam devices and from 0.1 to 1 mN for the cascaded devices. Measured bandwidths are [approximately equal] 700 Hz for both. The typical drive voltages used are [is less than or equal to] 12 V, permitting the use of standard electronic interfaces that are generally inadequate for electrostatic actuators. [592] Index Terms--Micromachining, micromotors, positioners, thermal actuators.