AfterTek

Scientists at Hewlett-Packard have discovered a new way to wire a certain type of computer chip, making way for an even smaller and cheaper electronics in the future. Although this chip-design breakthrough has been achieved only in laboratory simulations, Stan Williams, director of Quantum Science Research at HP Labs, said the company expects to make a working copy of the chip within a year.

The Palo Alto company’s advance shows that scientists are struggling to continue making smaller, faster and cheaper electronics as semiconductors start to approach the limits of Moore’s Law, which famously posits that the number of transistors that can fit onto a chip doubles roughly every 18 months.

Coined by chip pioneer Gordon Moore of Intel, this law of diminishing size has sparked a frantic race of innovation over the past 30 years, with scientists constantly trying to shrink the size of transistors and cram more on a chip.

“Moore’s Law is on a collision course with the laws of physics,” said Williams, who said HP’s breakthrough involves making chips smaller by shrinking not the transistors but the wires that connect them.  In brief, the basic working unit of every semiconductor is the transistor.

It is often likened to a gate. When open it registers “one” and when closed it signals “zero,” enabling the chip to speak the binary language of electronics. The more transistors on a chip, the more powerful it is.

For decades, the way to make chips smaller, faster and cheaper has been simple, Williams said: Make the transistors smaller. But at some point, transistors could become so small they’d be too costly. “The expense of fabricating chips is increasing dramatically,” HP researcher Greg Snider said.
HP is developing a way to shrink chips that does not involve shrinking transistors.

To understand its discovery, it’s necessary to back up one more step. The transistors in a chip are laid out like the buildings in a city. Streets and sidewalks connect the buildings. On a chip, wires rather than streets run from transistor to transistor. These connections make up a great deal of the surface of the chip, just as streets and sidewalks consume much of the surface area in a city.

What HP has done is create a wiring system that sits above the transistors instead of taking up valuable real estate between them. Thus, transistors can be packed closer together without having to make the individual transistors smaller. HP’s new wiring system involves a technical trick.

As Williams explained, it consists of two layers of conducting material, laid perpendicular to each other in a grid above the transistors. Between these two wires sits a third layer of material, such as soap, that is usually an insulator.

But HP has shown that by applying voltage to the top wire, it can force the insulator to conduct electricity. That is like throwing a switch. To turn off the switch, HP applies the same voltage to the bottom wire. At least for now, HP believes this new chip would be useful for field-programmable gate arrays, or FPGAs, a versatile type of chip used in cutting-edge electronics. But it is not suggesting that the same wiring trick would work for microprocessors or memory.

The reason has to do with the thinness of the new HP wires, which creates an inherent unreliability that FPGAs can tolerate. Bolsens, who has read an advance copy of the HP paper and is familiar with the company’s work, said the wires in its new system will be so thin, as measured in atoms, that a high proportion of the switches may not work. HP said it expects the “defect rate to be relatively high.”

But Bolsens whose firm is a leading maker of FPGAs, said the special nature of these chips means the defects could be tolerable. As the name implies, FPGAs can be reprogrammed after they are installed. So if a certain area of the chip is unusable because the connections are unreliable, it would be possible to route around the problem, he said.

Memory and microprocessor chips would not be so tolerant of wiring problems between transistors, so HP has designed its new technology for FPGAs. Bolsens said the ability to reprogram FPGAs makes them most useful in fast-changing products such as big-screen TVs, where the standards and protocols are often updated.

HP scientists are excited to have found a way to speed up the performance of at least this class of chips. Williams said the ground-level wiring between transistors now accounts for about 80 percent of the space on an FPGA. Changing to the second-story wiring scheme would recapture that space and make smaller, faster and cheaper FPGAs.