Posted 10/08/07 at 11:43:41 AM | by Tom Halfhill
The first electronic digital computers had thousands of vacuum tubes, but within 20 years, the bulky glass tubes were superseded by cool-running transistors. Now vacuums are making a surprising comeback. Eventually, I think all microprocessors will adopt this new technology.
IBM has announced that some of its future processors will use tiny “air gaps”—actually, vacuum cavities—to insulate their internal copper wiring. Today, all microprocessors use solid dielectric materials for this purpose. These conventional materials are easier to deposit during the chip-fabrication process, and they also provide physical rigidity and help conduct heat away from the circuits. However, as circuits keep shrinking, chip manufacturers are struggling to invent new solid dielectrics with good insulating properties. Denser circuitry leaves less room for the dielectric. Inadequate insulation causes short circuits that can be fatal to the chip.
IBM, Intel, and other companies are already introducing low-k dielectrics, which are advanced solid materials with improved insulating properties. Now IBM is going an important step further. By adding some innovative processes to an otherwise conventional fabrication line, IBM is creating microscopic gaps around the chip’s internal copper-wire traces. These sealed cavities contain near-perfect vacuums. A vacuum is the ideal insulator because it has the lowest possible dielectric constant, 1.0.
In practice, IBM’s vacuum dielectrics don’t quite reach the ideal dielectric constant because some solid dielectric material remains. IBM hasn’t perfected a manufacturing technique that removes all the solid material. However, removing all the material isn’t necessarily desirable at this point because it provides structural support and helps wick away the heat.
Vacuum dielectrics are a significant improvement, even when compared with low-k solid dielectrics. IBM says the vacuums can reduce the chip’s resistance-capacitance delay by as much as 35 percent. Designers can make processors that run faster without using additional power, or that use less power without sacrificing speed, or that achieve some combination of those improvements.
One part of IBM’s vacuum-gap technology is self-assembly nanotechnology, which has been widely misreported as tantamount to self-assembling chips. In reality, this technique is only one small step in the manufacturing process, in which a liquid material rearranges its molecular structure after deposition. It’s clever, but the tiny vacuums are the real story.
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