features and services such as HDTV, broadband communications, and advanced home security systems becoming more available through the use of optical fiber, wireless, satellite, and cable connections.

Paired with the growth in communications has been the growth of computers and information processing. The GPS receivers and wireless phones available today use the latest in integrated circuit technology. AMO science is playing a key role by enabling the increase in the density and speed of computer chips. As an example of what is possible even today, a tiny transistor component on a chip is shown in the electron microscope image in the box “Laser Lithography.” This transistor would easily fit inside a bacterial cell.

Computer technology continues to advance, resulting in everfaster computation speeds. This progress is based on the decreasing size of the transistors in the very-large-scale integrated (VLSI) circuits used in computers and signal processors. Transistor feature sizes in commercial production have been decreasing, from 0.35 microns in 1995 to 0.13 microns in 2002. These dimensions are nearly 1/1,000th the diameter of a single strand of human hair. One important factor limiting feature size on a chip, and thus the computational speed, is the wavelength of the light used to form the transistor patterns and interconnecting wires. The shorter the wavelength, the smaller the features.

LASER LITHOGRAPHY

A top-down scanning electron microscopic view of a field-effect transistor gate (green rectangle) where the source and drain for the device (narrow blue horizontal lines) are spaced by only 0.12 microns (a human hair is approximately 100 microns wide). These ultrasmall features are patterned by photolithography. Photolithography uses a patterned mask in combination with an excimer laser with a wavelength of 248 or 193 nanometers. The beam from the laser is focused through the mask to expose the features seen above. This transistor is a component in a digital signal processor fabricated at Bell Labs. It operates at 100 megahertz and uses only a 1-volt power supply. Potential applications include enabling smaller and lighter cellular phones with extended battery life. The technology also could be instrumental in data transport over wireless phones, in higher-speed Web surfing, and in video applications.

Today, ultraviolet excimer lasers with average output powers in the 20-watt range are replacing the older mercury arc sources. It is interesting to note that it would take more than a billion 100-watt incandescent lightbulbs on at the same time to be effectively as bright as this laser source. Excimer lasers operate using the light emitted from gas molecules excited in an



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