May 3, 2000 A novel fabrication technique developed at the University of Illinois could provide a reliable and robust method for assembling large arrays of three-dimensional microstructures.
"Like origami -- the Japanese art of folding paper into complex shapes -- our technique works by folding together small pieces of material," said Chang Liu, a professor of electrical and computer engineering and director of the Micro Actuators, Sensors and Systems Laboratory at the UI. "But the pieces we work with are very tiny -- about 100 microns on a side -- so we use a magnetic field instead of our fingers to fold them into shape."
To fabricate arrays of 3-D structures, individual components are first cast in place on sacrificial layers using planar deposition. A small amount of magnetic material is electroplated onto each of the parts, which are then freed from the substrate by a highly selective etchant. When a magnetic field is applied, the induced torque causes the pieces to rotate out of the plane on tiny hinges and lock into place.
"By varying the amount of magnetic material attached to the flaps, we can control the speed at which the parts fold into position," Liu said. "This creates a sequential assembly process that can significantly improve the speed and efficiency of fabricating large arrays of 3-D structures."
Magnetic actuation could be used to create arrays of neural probes, micro-optical devices or miniature testing devices for integrated circuits, Liu said. The unique fabrication process also makes possible the development of a modular building block for the construction of a new class of integrated micro-sensors.
"The development of a micro-integrated sensor typically takes many years and costs millions of dollars," Liu said. "As yet, there are no 'off-the-shelf' components to be used in construction, so each sensor must be custom built. To develop sensors faster and cheaper, we need to use standard parts that can be mass produced in a process similar to that used in the integrated circuit industry."
With funding from NASA, Liu has recently teamed up with UI entomologist and neurobiologist Fred Delcomyn to develop a micro-integrated sensor that mimics the action of a hair cell.
"The hair cell is a very fundamental structure consisting of a long cilia attached to a neuron," Liu said. "Nature uses this basic building block in a variety of ways to accomplish such sensing tasks as hearing, balance and touch."
The use of microelectromechanical fabrication techniques offers unique opportunities for creating artificial hair cells with a size scale and frequency response comparable to their biological counterparts, Liu said. The resulting sensors could be used in many applications, including autonomous robots that more fully perceive and respond to their environment.
"The magnetic actuation of hinged, micro-machined structures may provide a type of standard tool box that could dramatically improve the efficiency of modern sensor development," Liu said.
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