doubles every 18 months. Intel's original microprocessor, intro- duced in 1971, had 2,300 transistors. Top-of-the-line computers in 2001 contained some 42 million transistors that performed 100 billion operations per second. Today, Intel's high-end chip contains more than 1.7 billion transistors, and that number is expected to exceed 10 billion by 2010. Unfortunately, there's also an awful truth about Moore's Law. Today's transistors are about a micrometer in overall length, which means dozens of them could sit on top of a human red blood cell. This very success is bringing chipmakers to the brink of a new, steep obstacle to further gains in performance. The problem lies in the tiny metal wires that weave the transistors into integrated circuits. For the sake of illus- tration, consider that the Intel 130-nm Pentium IV processor chip contains 55 mil- lion transistors and uses roughly 3 miles (4.8 km) of interconnects to support each square centimeter of its circuitry. With the introduction of 90-nm microprocessors, the chips house 110 million transistors and nearly 4.25 miles (6.9 km) of intercon- nects per square centimeter. Today's most advanced integrated circuits switch up to 10 billion times per second, and their metal interconnects can barely keep up. Each new generation of chips makes the situation worse. While interconnect delay times are stretching out, transistor switching is getting faster, sending more sig- nals down slow lines. Additional trouble areas include heat buildup, electrical cur- rents leaking out of circuits, and electrical crosstalk between neighboring wires. Copper, the traditional interconnect technology, is running out of speed. The good news is that the industry is working on several solutions. Two main approaches are emerging: one designed to change the propagation characteristics of those tiny on- chip transmission lines and the other involving the development of silicon photonics. Researchers are developing thin films that have a lower dielectric constant (k) than the silicon dioxi