Mike Davidson knows art when he sees it. But he didn't expect to see it on a microchip. One day about six years ago, the senior research engineer was quietly working away in his lab at the National High Magnetic Field Laboratory at Florida State University, in Tallahassee, taking photographs for his annual chip-shot calendar, which features microscopic images of microchips. To fit as much of a MIPS R4000 chip as possible into a single photograph, he set his high-powered Nikon FX/L optical microscope at a relatively low magnification, between 25X and 100X. Then, to make the circuitry "pop" for a more richly detailed photo, he lit large areas of the chip with a tungsten-halogen light and increased the magnification to 600X. Suddenly, he saw a face [see photo, above].
To Davidson's eye, the preternaturally long mug, round spectacles, lumberjack hat, and flyaway hair looked just like Waldo, the then-ubiquitous cartoon character of "Where's Waldo?" fame. "I realized it wasn't part of the integrated circuitry," Davidson said, "but I thought it might be something the engineers had put on the chip to thwart anybody trying to reverse-engineer it."
Intrigued, he posted photographs of Waldo on his Molecular Expressions Web site, home to microscopic images of everything from beer bottle labels to DNA. Soon after, he was contacted by the image's creator, chip designer Kevin Kuhn, who worked at MIPS Technologies Inc., Mountain View, Calif.
"He told me it wasn't really Waldo [but] another designer at MIPS," Davidson told IEEE Spectrum. "He said it was just artwork that he had put on the chip because he had spent such a lot of his life working on the chip." Kuhn called it a sort of signature and told Davidson to look for other images on the chip, including a license plate containing the chip number and its version [see photo, above].
What started out as a serendipitous discovery became a passion for Davidson. He began looking for and collecting images he found on other chips and putting them on what he now calls the Silicon Zoo portion of the Molecular Expressions Web site (http://micro.magnet.fsu.edu/creatures/index.html). As word about the site got around, design engineers from all over sent Davidson chips and wafers, hoping to preserve their silicon creatures for posterity. Now the Zoo features the ersatz Waldo along with 300 other pieces of what is variously termed chip art, artifacts, or graffiti.
The images include everything from chip designers' names, renderings of favorite pets, cartoon characters like Dilbert, and planes, trains, and automobiles. These images are fabricated along with the transistors and interconnects on one or more metal layers overlying a silicon wafer. First, the image is drawn on a mask used to make a pattern in photoresist overlying a metal layer, usually the first. Through the gaps in the mask ultraviolet light is shone onto the photoresist, hardening what it exposes. A solvent washes away the soft remainder, exposing areas of aluminum to etching in their turn. Lastly, the hardened photoresist is washed off with acid, leaving an image in metal.
Many of the creatures housed in the Silicon Zoo Davidson found on small-run video and graphics chips dating from the late 1970s and early 1980s. Back then chip graffiti was more abundant, in part because it thwarted illegal copying, said Louis Scheffer, a former chip designer with Hewlett-Packard Co. and now a fellow at Cadence Design Systems Inc., San Jose, Calif. If someone stole the chip design by simply copying the masks, the graffiti would be copied, too, and give the thief away.