From: believer@telepath.com Subject: IP: Neural Computer to Rival Brain??? Date: Thu, 08 Oct 1998 09:15:57 -0500 To: believer@telepath.com Source: The Economist http://www.economist.com/editorial/freeforall/current/index_st4636.html SCIENCE AND TECHNOLOGY Semiconductors - Silicon smarts BRAINS and computers are very different things. Brains consist of a trillion or so tiny elements, called neurons, which are individually dumb but collectively, thanks to the thousand trillion connections between them, very powerful. Most computers, on the other hand, depend on a single, complex component-a microprocessor-to get things done. Even the most advanced supercomputers, with hundreds or even thousands of connected microprocessors, cannot match the compactness or connection density of the human brain. Two new chip-making techniques being developed at Irvine Sensors Corporation (ISC) in Costa Mesa, California, could be significant steps in the long-running effort to make more brain-like computers. Researchers at ISC have found a way to pack silicon chips extremely tightly together and, better still, to make large numbers of connections between them. Their technique layers silicon chips on top of each other, cramming 50 chips into the space normally occupied by just one. This is done by grinding away the underside of the silicon wafer on which the chip circuitry is built-a thick, non-functional platform that can be removed without affecting the chip's operation. The result is a paper-thin but fully functional chip, which can be stacked and bonded with other chips to form a single unit. The chips are wired together via connectors along their edges, and the whole sandwich is embedded in epoxy resin. This space-saving technique is already being used commercially in a four-layer memory chip that packs 128 megabits of data into an amazingly small one-centimetre-square package. Earlier this year, ISC won a $1.3m military contract from Boeing to build a wearable, voice-activated computer the size of a pack of cards. But while such stacking wizardry means computers can be smaller, it does not make them more brain-like. At present, the nearest approximation to a silicon brain involves making electronic circuits that behave like neurons, and connecting them up in small networks. Such "artificial neural networks" can be used for everything from image recognition to credit scoring, but their size and complexity-and so their deductive power-is limited. This is because it is only possible to fit a certain number of silicon neurons on to a single chip; and there is a limit to the number of connections that can be made between adjacent neural chips. Researchers would like to be able to build networks that are larger and more densely connected-in short, more brain-like. ISC's second technology should let them do this, by allowing direct vertical connections to be made anywhere on the adjoining surfaces of adjacent chips in a stack. To achieve this, half of a special component called a three-dimensional field-effect transistor, or 3DFET, is constructed at the site of each connection, as part of the usual chip-making process. When the chips are stacked, the two halves of each 3DFET fit together, allowing signals to pass up and down from one chip to the other. A prototype 3DFET, developed with financing from the US army's ballistic missile defence organisation, has already been made and tested. With new funding, ISC hopes to make a chip-stack connected using 3DFETs within 18 months. After that, says ISC's chief technical officer, John Carson, the long-term goal is to stack 1,000 neural chips in a single cube. This would involve thinning each chip down to less than the thickness of a human hair. Already, ISC has produced a prototype that is almost this thin. If ISC can squeeze a million silicon neurons on to each chip, and pack a thousand chips into a one-inch neural cube, the arithmetic starts to get interesting. A thousand such cubes, which could fit in a shoebox, would contain a trillion neurons, and a hundred trillion connections. That would still not match the connectivity of human grey matter. But it would be the most brain-like computer ever made. ----------------------- NOTE: In accordance with Title 17 U.S.C. section 107, this material is distributed without profit or payment to those who have expressed a prior interest in receiving this information for non-profit research and educational purposes only. For more information go to: http://www.law.cornell.edu/uscode/17/107.shtml ----------------------- ********************************************** To subscribe or unsubscribe, email: majordomo@majordomo.pobox.com with the message: (un)subscribe ignition-point email@address ********************************************** www.telepath.com/believer **********************************************