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ScienceDaily (May 22, 2009) — Chip manufacturers beware: There's a newfound flaw in our understanding of transistor noise, a phenomenon affecting the electronic on-off switch that makes computer circuits possible.
While exploring transistor behavior, the team found evidence that a widely accepted model explaining errors caused by electronic "noise" in the switches does not fit the facts. A transistor must be made from highly purified materials to function; defects in these materials, like rocks in a stream, can divert the flow of electricity and cause the device to malfunction. This, in turn, makes it appear to fluctuate erratically between "on" and "off" states. For decades, the engineering community has largely accepted a theoretical model that identifies these defects and helps guide designers' efforts to mitigate them.
May 22, 2009, 8:01 am
Counting Down to the End of Moore’s Law
By Saul Hansell
“We’re looking at a brick wall five years down the road,” Eli Harari, the chief executive of SanDisk, said to me earlier this week.
Normally, when I’ve talked to chip executives about the limits of Moore’s Law, they are confident, in a vague sort of way, that they will be able to continue to increase the capacity of their chips one way or another.
Mr. Harari was a great deal more precise about the brick wall his company is heading toward: “We are running out of electrons.”
“When we started out we had about one million electrons per cell,” or locations where information is stored on a chip, he said. “We are now down to a few hundred.” This simply can’t go on forever, he noted: “We can’t get below one.”
SanDisk and other flash memory makers have figured out how to cram even more information into that tiny cell. Until a few years ago, each of those cells worked the way most computer memory does — it represented either a zero or a one. Now the chip can actually count how many electrons are in a cell, and depending on the number it can write and read up to 16 states (recording a number between zero and 15, or four bits to a computer).
The problem here is that the way current flash technology stores those electrons, they don’t always follow instructions, especially as the memory card gets older.
“When you have a billion cells, you cannot uniformly control them to one electron,” Mr. Harari said. “If I want 40 electrons, plus or minus two electrons, I can do that when the device is new. But seven years out, it will start to smear.” In other words, the electron count will start to vary from one cell to the next.
SanDisk, to steal a line from a bigger Silicon Valley company, has an app for that. The controllers on each of its chips keep track of these errors and compensate for them.
There is still some more engineering to do. The company can try to make cells smaller, get more bits per cell and improve the controllers.
But at the end of the day, Mr. Harari said, it probably can double the capacity of its chips only two more times. Once the industry goes from its current 64-billion-bit chip to a 256-billion-bit chip (that’s 32 gigabytes), it will hit that brick wall.
Your camera and music player will certainly be able to store a lot of files. But you won’t be able to count on next year’s iPhone having double the capacity at the same price.
He may be heading for a brick wall, but Mr. Harari has a plan: Head up.
“When Manhattan ran out of space, they built skyscrapers,” Mr. Harari said. “It’s the same for us.”
Right now semiconductors are all based on the particular properties of circuitry etched onto a flat piece of silicon. Four years ago, SanDisk bought Matrix Semiconductor, a company that was trying to develop a way to stack multiple layers of very tiny memory cells on top of one another.
(SanDisk is far from the only company trying to explore the third dimension in flash memory. Bill Watkins, the former chief executive of Seagate, recently joined the board of a company, Vertical Circuits, that uses a silver ooze to stack memory chips.)
Mr. Harari said the company’s engineers were making good progress. But he didn’t have the Pollyanna view of some chip executives that Moore’s Law will apply forever.
“When you have a new material, all bets are off,” he said. “Until you have it, you don’t have anything.”