Technology Bulletin

November 16, 1998

Universal substrate builds better lasers/thin-film devices

The race to build lasers and other optoelectronic devices on a compliant universal substrate appears to be over. Since 1996, when the concept was first proposed by scientists at Cornell University, research groups around the world burned candles into the night in an attempt to be the first to find a better way to make high performance semiconductor devices. A joint research team from the University of Houston (UH), Applied Optoelectronics Inc. (AOI), and Cornell University won. The new technique for creating epitaxial thin-film devices, recently unveiled at the North American Molecular Beam Epitaxy Conference, "will allow us to create lasers and optoelectronic devices with better performance and lower costs by relieving a lot of the materials constraints," says Steven Pei, associate director for research at the Space Vacuum Epitaxy Center (SVEC), the NASA Commercial Space Center at UH. Epitaxy grows single crystal materials on a base or substrate with atomic precision. A combination of layers might produce a laser, while another combination could result in a high-efficiency solar cell. Traditional epitaxy requires that the substrate's crystalline structure matches the material being placed on top. Currently, only a few substrate materials are available, fewer still are affordable. The "compliant universal substrate" resembles a grid printed on a piece of rubber loosely bonded to a conventional substrate. It expands or contracts to match the grid of the epitaxy thin film grown on top of it. By eliminating concerns about matching the grids on the underlying conventional substrate, the universally compliant substrate could dramatically increase the choices of epitaxy thin films/substrate combinations for optoelectronic applications. It may even lead to less expensive base/substrate materials, say the researchers. The NSF, Air Force, and Ballistic Missile Defense Organization are funding the research to develop semiconductor mid-infrared lasers for environmental monitoring and jamming of heat-seeking missiles. E-mail:

Secure your computer against hackers with a 'real' lock

Researchers at Sandia National Labs (Albuquerque, NM) dealt a severe blow to potential computer hackers when they debuted the Recodable Locking Device. Made with microelectromechanical systems (MEMS) technology, the lock consists of a series of tiny notched gears that move to the unlocked position only when the owner enters the right code. Dubbed the "world's smallest combination lock," the device may be the first mechanical hardware designed to keep unwanted guests from breaking codes and illegally entering computer and other secure systems, say researchers. The device consists of six code wheels, each less than 300 microns in diameter, driven by electrostatic comb drives that turn electrical impulses into mechanical motion. The lock owner sets a combination to any value from one to one million. The entire mechanism, about the size of a button, measures 9.4 mm @ 4.7 mm. The lock has a secure side and a user side. To unlock the device, the user must enter a code that identically matches the code stored in the code wheels. After one failed try, the device mechanically shuts down and cannot be reset except by the owner on the secure side. Sandia demonstrated prototypes

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