Cell phones have been a big hit because they untether communications technology from the desk, giving anyone that capability anywhere. The logic of this trend would suggest that the next step might be to implant a tiny cell phone-on-a-chip directly into the cerebral cortex. With dense electrode connections to the speech center of the brain and RF communications to the nearest Wi-Fi hotspot, it would be the next best thing to being psychic.

Sound extreme? Maybe. But this is a pivotal moment in the history of electronics, when technology is morphing from something that extends the body to something that merges with it. Electronic components can shore up faltering human capabilities, in the form of artificial limbs that use real-time embedded control, implantable defibrillators that correct the heart's rhythms, and artificial ear and eye systems that help the deaf and the blind.

"There are a variety of people in the investment community, and I share their view, who believe that this century is clearly the century of the 'bionic man' — the human being whose life style has been improved substantially through the use of these electronic enhancements," said

Nicholas Colella, senior vice president in the Product Miniaturization Division at Tessera Inc. (San Jose, Calif.). Tessera has been developing miniaturized chip-scale packaging over the past 10 years, a critical technology in this area.

Yet, for all their promise, the developments in implant electronics also carry profound implications for medicine and ethics. On a more mundane level, they present major design challenges. Connecting inorganic silicon circuits to the delicate nerve nets of the body poses a host of problems in itself. And then comes the hurdle of building safe, highly compact, extremely low-power components that can exist independently in the body for decades.

The market, meanwhile, has barely begun. Cochlear implants — hearing aids that link directly to the auditory nerves in the ear, while the rest of the system is worn externally — are now being marketed as products, but vision research, which is inherently more difficult, is still in the R&D stage. Compact vision systems that can be worn on glasses and connect directly to the optic nerve have been demonstrated. Elsewhere, implantable control systems that monitor and correct heart function have become common. Further down the road are electrode implants that would cure paralysis resulting from nerve damage.

The quest to heal such ills has the blessing of large institutions like the National Institutes of Health, hospital research centers and charities. It also has a feel-good component that makes it possible to accept — or at least contemplate — the idea of rather bizarre intrusions into the body. But when the usual dynamic of commercialization takes hold, ethics and conventional morality tend to work against the notion of the bionic man.

Consider, for example, a small step toward such futuristic visions of im-plantable electronics: A couple of years ago, a number of individuals volunteered to have radio frequency ID tags implanted under their skin. This is a medically benign operation, but the social implications are a little scary. The demo project touched off a heated debate over issues such as personal privacy and whether the body should be declared off-limits to invasive technology.