Stacking chips without wires and solder: "Everybody complains about the long wires on circuit boards that limit the speed of inter-chip communication. But, now engineers at Sun Microsystems [have] eliminated the need for them entirely.
Sunís solution is to put the chips close enough to one another so that they can communicate directly, without using wires at all. Called proximity communication, the technique is the brainchild of Sun vice president Ivan E. Sutherland, best known for cofounding Evans and Sutherland, a groundbreaking computer graphics company, back in the late 1960s. The technique, explains Robert Drost, a principal investigator on the project, relies on capacitive coupling. "When two conducting structures are close to one another, an electrical signal on one of them causes an electrical signal to appear on the other," he says.
So, in place of the conventional output pads to which wires would be bonded, the engineers built an array of small metal plates, 50 nm on a side, above the top wiring layer of a chip, covering the entire chip with a micrometer-thick protective layer called a scratch coating. [When] two chips face to face so that the metal plates lined up, allowing the plates to communicate with their counterparts capacitively through two thicknesses of the scratch coating. To use this approach in a system with many chips an upper array of chips, spaced slightly less than a chip-width apart, would overlay a bottom array. The two arrays would be offset so that each corner of a chip in the upper array overlaps a corner of four chips in the lower array .. "That allows you to build a two-dimensional system of arbitrary size," Drost explains."
Advantages: higher data rates, lower power, and replacement of faulty chips without soldering.
"No plans are yet in place to commercialize the technology. Sun is developing the technique under a contract with the U.S. DARPA. .. More than one company is seeking ways to speed up interchip communications. In August 2002 Infineon Technologies AG announced a new method of connecting stacked ICs in 3-D packages .. The Infineon approach uses small copper pads on the tops of the chips and puts them face to face in the package .. with a thin layer of solder, making a direct electrical connection ..The first wafers to use this technology are being processed now with the first products expected in 2004." 11:00:06 PM
Wireless Networks Gain Spectrum: Controversy over its usefulness over long distance: "The Federal Communications Commission set aside a new slice of airwaves yesterday for wireless Internet users, a move the agency said was designed to encourage the spread of high-speed data access in rural and other underserved areas. ..
Some public interest groups criticized the FCC's decision yesterday, saying the particular slice of airwaves targeted by the agency is not well suited for delivering a robust, high-speed data stream to a wide area. They argued that the 255 new frequencies can't carry a data stream capable of penetrating walls or even passing through leafy trees. .. But FCC officials said several start-up companies have already demonstrated that the new frequencies can deliver data over relatively long distances. "I have no idea where they get their information, but they [the signals] can go five miles," said Edmond Thomas, FCC chief of engineering and technology." 10:45:08 PM