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Assembly Method for Three-Dimensional MEMS Saves Chip Space Using Single Magnetic Actuation for Large Arrays of Devices Office of Technology Management U N I V E R S I T Y O F I L L I N O I S AT U R B A N A – C H A M PA I G N Technology Summary This technology is an efficient process for assembling large arrays of three-dimensional, hinged micro structures for micro electromechanical systems (MEMS) applications. Using a single electromagnet for actuation, this new method saves chip space as well as actuates large arrays of devices in parallel. It makes fabrication of MEMS devices more reliable and simple by eliminating the need for biasing several actuators and not requiring a constant source of energy for actuation. Thousands of microstructures, each measuring less than 0.1 mm, can be assembled in parallel within 10 sec. While MEMS fabrication has been the primary area of study, this method also can be a general process for assembling many types of three-dimensional structures. Benefits This new method for assembly of MEMS devices eliminates the need for individual biasing of actuators, saves chip space, and doesn't require a constant energy source. • Added reliability and ease of assembly: A single electromagnet actuates a large array of devices in parallel. • Biasing eliminated: The method eliminates any need for individual biasing of the actuators. • Lower energy needs: The method does not require a constant source of energy (constant actuation) to maintain MEMS flaps in an off-plane position. • Less chip space required: Smaller die sizes and, ultimately, larger area densities can be used on integrated, optical MEMS. Applications • Optical MEMS (e.g., micromirrors, switches, waveguides) • Micro sensors (e.g., flow rate sensors) • Micro probes (e.g., IC testing probes) Patent Information The technology holds a U.S. patent. http:// www.otm.uiuc.edu/technology.htm Technical Details This novel technology is a sequential assembly process that allows fabrication and assembly of large arrays of three-dimensional, hinged MEMS. The ability to use a single electromagnet for actuation saves chip space and actuates large arrays of devices in parallel—making fabrication of MEMS devices faster, more reliable, and more cost-effective. Another variation of this method involves using a MEMS assembly with one flap that has a spring beam (an offset slab). This spring beam increases the magnetic field strength needed to raise the flap and also causes the flaps to operate asynchronously in an increasing magnetic field. The spring beam also provides variable resistance to the flap when it is positioned at different angles. Why it Is Better How it Works The process is used with a MEMS assembly that includes at least one hinged flap. The individual components are cast in place on sacrificial layers, using planar deposition to electroplate small amounts of a magnetic material, such as Permalloy, onto each part. The parts are then freed from the substrate by a selective etchant, after which a magnetic field is applied to cause the pieces to rotate out of the plane on tiny hinges and lock into place. Varying the amount of magnetic material applied to the flaps allows control of the speed at which the parts fold into position. Because of their differing amounts of magnetic material, the flaps are raised asynchronously when placed in an increasing magnetic field. They also can be designed to remain interlocked after the magnetic field is removed, thereby enabling use of a single magnetic field that does not require actuators on the chip itself. In order to maintain off-flap displacement, previous methods have required dedicated, on-chip micro-actuators that are mechanically, electrically, or magnetically linked to the flap and that supply a constant energy source to the structure. This new technology uses only a single electromagnet to actuate many devices asynchronously. Previous methods that required individual actuators to deploy large arrays of devices were compromised because each actuator had to be individually biased. By eliminating that need, this new method provides easier, more reliable assembly. Most current actuators occupy a large portion of the chip area (approximately 100 µm2), in addition to the flap itself, thereby increasing the die size and limiting the ultimate area density of integrated optical MEMS. The chip space saved by this novel process translates to time, materials, and cost savings. ■ contact: Roger VanHoy; (217) 244-1275; [email protected] D&T File Number: T99017 [UI01-044] 2.28.03; T99017 [UI01-044]