Electrothermal actuation is not a popular technology for today’s MEMS transducers due to its relatively slow response and large appetite for power. The large displacement with high force and low voltage gives reason to try to improve thermal actuator’s operating characteristics. This paper describes some improvements to thermal actuators, mainly in increased output energy per actuator chip area and area utilization. The devices presented here are a variation of the chevron thermal actuator - one with two sets of thermally expanding beams pushing at a slight angle on either side of a suspended shuttle, causing it to be displaced parallel to the substrate. One improvement is to taper the thermal expansion beams so they exhibit a higher strain energy, allowing a larger thermal input power and hence more output mechanical power per beam. Another improvement is to move (fold) both sets of thermal beams to the same side of the shuttle so all are exerting force on the same side. The thermal expansion beams cause compression against the shuttle and work against one or two orthogonal cold beams in tension to produce an output force and displacement. This resembles a pseudo-bimorph array with the exception of having far fewer non-force-producing beams to bend.
Micromirrors with linear deflection behaviors have been found useful for systems requiring 1D and 2D optical scanning patterns and are solutions for low-cost vector or video raster image generators. The advantages of thermal buckle-beam and bimorph actuators are high resulting force, low MEMS area and low voltage requirements. The devices presented in this paper can achieve modest deflection angles at relatively high frequencies. The mirror actuators consists of a doubly clamped array of polysilicon beams that are Joule heated and allowed to buckle out-of-plane. Instead of utilizing the usual linear displacement, a torque is derived from a coupling beam attached across the buckling beams at the point of the maximum derivative of buckle. As the beams buckle, the torque causes the mirror to be rotated away from the substrate. Non-resonant, near-linear mirror deflection response has been achieved with a maximum deflection of six mechanical degrees at a frequency of a few KHz. Employing a high Q resonant structure, a frequency of 16 KHz has been attained with a 1D mirror scanner at a maximum mechanical deflection of around 20 degrees. 1D and 2D scanning mirror devices have been built and will be reviewed in this paper.
Conference Committee Involvement (4)
Device and Process Technologies for Microelectronics, MEMS, and Photonics IV
12 December 2005 | Brisbane, Australia
Smart Sensors, Actuators, and MEMS II
9 May 2005 | Sevilla, Spain
Micro- and Nanotechnology: Materials, Processes, Packaging, and Systems II
13 December 2004 | Sydney, Australia
Smart Sensors, Actuators, and MEMS
19 May 2003 | Maspalomas, Gran Canaria, Canary Islands, Spain
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