Tools for Getting Smarter

Cell phones. The screen in your laptop. “Many of the electronics that we see getting smaller,” says Susan Trolier-McKinstry, “are using smart materials.

orange switch on orange
Qingqi Zhang and the U.S. Army and Northrop Grumman.

Smart circuits and switches keep getting smaller. A piezoelectrically-actuated switch.

dark gray-blue microscopic image of lever
Qingqi Zhang and the U.S. Army and Northrop Grumman.

A scanning electron microscope (SEM) image of a micromachined cantilever.

microscopic image of yellow and green against brown
Qingqi Zhang and the U.S. Army and Northrop Grumman.

An optical microscope photo of a piezoelectrically-actuated bridge structure.

“Smart materials are materials that sense changes in the environment and react to those changes in a useful manner,” explains Trolier-McKinstry, director of the W. M. Keck Smart Materials Integration Laboratory at Penn State. Applying an electric field, for example, will cause some smart materials to lengthen. Conversely, when put under pressure that flattens them, these same materials create electric signals. In your laptop, this property is used in piezoelectric transformers that allow the screen to be as thin as a notepad.

Piezoelectric materials have distinct centers of positive and negative charge. Applying an electric field causes the negative and positive charges to expand away from each other: the material elongates. One familiar application of this property is in biomedical ultrasound. When an alternating electric field is applied, the piezoelectric material expands and contracts, emitting a sound wave. “When the sound waves bounce off an object and return,” Trolier-McKinstry explains, “the material is in a listening mode.” Under the pressure of the returning blip, the positive and negative charges are pushed back together, creating a new signal. This information can be used to make a picture of the object under study.

If a piezoelectric material is made to rapidly expand and contract, creating quick successions of sound waves, it creates a buzz. This property can be used in tiny speakers, like those in the ear-piece of your cell phone.

Some optoelectronics are also smart materials. Like piezoelectrics, electrooptic materials react to an electric field. But instead of conveying sound, they convey light, similar to fiberoptics. What makes electrooptics “smart” is that the light waves conveyed inside them can be made to bend, and so can be rerouted, much like a train switching tracks. An optical switch can be used in a variety of technologies. “With fiberoptics running to your house, and an efficient system for optical switching,” Trolier-McKinstry says, “video-on-demand would be a much more advanced system.” It could include a wider array of programs, and offer them at a continuous set of times.

The next step in smart materials research is to combine piezoelectrics and electro-optics into a single device. “The dream is to develop a photostrictive device,” says Trolier-McKinstry, which would change shape when exposed to specific frequencies of light. Such a device could be applied, for instance, to space antennae. Thus, an optical signal would initiate a sequence of changes in the shape, causing the antenna to refocus on a different point in space.

Researchers at Penn State are also working on designing robots that are activated by light. Already, a bipedal stand made of photostrictive materials is able to “walk” when exposed to light.

Penn State's interdisciplinary research program in materials has been a leader in the study of smart materials for over 30 years, says Trolier-McKinstry. A typical approach has been for researchers to begin with knowledge of the fundamental properties of known materials. “Then we design and synthesize these new materials and see how they work,” Trolier-McKinstry explains. Measuring the dielectric, electro-mechanical, and optical properties of the new material tells a researcher where and how it might be applied constructively. Taking the next step towards implementing those ideas into components—and actually creating prototypes of next-generation devices—is the goal of the Keck Lab.

The lab's facilities include a class 100 clean room housing a machine called a contact aligner, which allows intricate patterning of photo-resist materials, a step in the making of circuits and switches. The clean room also has wet benches where photo-resist patterns can be transferred to materials of interest. The room is intended for processing of a wide variety of materials, including those that would be difficult to introduce into a conventional silicon-based clean room. Additional facilities include a sputter deposition tool for depositing thin films; a suite of tools for thick-film processing; and a micropen designed to deposit thin, even layers of active inks to create “precision deposited images,” which are essentially circuits that are drawn rather than built, allowing for the rapid redesign of circuitry to speed up the prototyping process. The lab is located in the Materials Research Lab building.

“Historically, one of Penn State's strengths has been materials design,” Trolier-McKinstry states. “The Keck Lab is to make us better at prototyping. The lab represents a fundamental change in the scientific infrastructure of the University.”

Susan Trolier-McKinstry, Ph.D., is the Corning Faculty Fellow of Ceramic Science and Engineering and director of the W. M. Keck Smart Materials Integration Laboratory, 151 Materials Research Lab, University Park, PA 16802; 814-863-8348; STMcKinstry@psu.edu. The laboratory is funded by the W.M. Keck Foundation, Penn State's Center for Dielectric Studies, and Motorola. It is open to any researcher affiliated with Penn State, and available to industry professionals on a fee basis.

Last Updated January 01, 2003