image



An Eye into the Cosmos

In 2013, NASA will launch the James Webb Space Telescope (JWST) one million miles out into space, four times farther from the earth than the moon, and 2,500 times farther than its predecessor, the Hubble Telescope.

The JWST will be like no telescope before it. A perfectly positioned space laboratory, it will observe the deep universe by blocking out the brighter light of closer objects to capture the faint light of vanishing galaxies. Its centerpiece is a near infrared spectrometer, one of many new instruments invented for the telescope. The spectrometer will focus on the faint glow of faraway galaxies by utilizing a waffle-like grid of microshutters.

Lehigh is playing a critical role in designing the microshutters that will help the JWST capture selected infrared signals from the edge of the universe and thus observe the most distant galaxies. The JWST spectrometer will focus on the faint glow of faraway galaxies by utilizing a waffle-like grid of some 250,000 microshutters. Each waffle cell is covered by a microshutter measuring 100 by 200 microns, or the width of several human hairs, and each one can be opened or closed individually. This enables the telescope to view — and block out — selected portions of the sky.

To receive weak infrared light signals from selected points at the edge of the universe, some microshutters must remain open for days at a time. In these cases, a 40-volt electrostatic charge will be applied to "latch" the microshutter to the cell wall and prevent it from closing after the magnet is removed. This prolonged opening, however, can cause the microshutter to lock in the open position after the applied voltage is withdrawn. The problem, called "stiction," causes NASA to lose control over the microshutters.

To solve stiction, NASA turned to James Hwang, professor of electrical and computer engineering and director of Lehigh's Compound Semiconductor Technology Lab. Working with three undergraduate electrical engineering majors, Hwang discovered the reason for the stiction — the voltage applied to keep the microshutter lid open was causing dielectric charge to be trapped in the cell's silicon-nitride insulator.

"When you hold the microshutter open for several days at a time, charge starts to build up in the insulator," says Hwang. "Normally, to close the microshutter, you remove the voltage and it springs shut. But a charge that is trapped in the insulator is sufficient to keep the microshutter open.” Hwang and his team established that the dielectric charging can cause stiction, and are recommending that NASA use a bipolar voltage to the microshutter with alternating applications of positive and negative voltages and thus canceling the trapping of the charge in the silicon-nitride insulator.

Rob Guzzon, Andy Melchior and John Yamrick, the undergraduates who investigated the stiction problem, traveled to Maryland to use the Goddard Space Flight Center (GSFC) cryogenic testing equipment. Guzzon is now a Ph.D. student at the University of California-Santa Barbara. Melchior works for Thales, the international electronics and systems group, on a MEMS project related to software-defined radio. Yamrick is completing a second B.S. at Lehigh, this one in engineering physics.

"I relied heavily on all three students," says Hwang, who also supervises six Ph.D. candidates and four postdoctoral researchers. "Even though they were undergraduate students, they were ready to take on independent research and be treated like Ph.D. students."


To learn more about this project and the broader Lehigh-NASA partnership, see “A Match Made for the Heavens” in Resolve™ magazine (volume II) – a publication devoted to Lehigh engineering research and educational innovation, highlighting exciting partnerships, projects and academic programs within and around Lehigh's engineering community.

 
NANOTECHNOLOGY AND APPLICATIONS