‘Stacked’ Chips Could Replace Hard Drives

By David L. Brown

As applications and databases grow ever larger and more complex, computers demand more and more memory. Hard drives are reaching the limits of how much data they can hold — but a solution may be coming soon. It’s all to do with the idea of ‘stacking’ memory chips to increase density, much as a can of Pringles can hold as much as a large bag of edible chips.

According to a report from Arizona State University, Tempe, a team led by Dr. Michael Kozicki has developed just such a way to “stack” memory layers on a single chip to make high-density memory modules.

“This could lead to hard drive data storage on a chip,” Kozicki said, “which enables portable systems that are smaller, more rugged and able to go longer between battery charges.”

Imagine the capacity of a full-sized hard drive on a tiny chip that could reside in a cell phone or other portable device. Not only may that be possible, but Kozicki says the stacked memory chips are simple and can be made using present technology and materials.

Kozicki is a professor of electrical engineering and director of ASU’s Center for Applied Nanoionics, devoted to studying nano-scale electronics. Graduate student Sarath C. Puthen Thermadam also worked on the project.

Memory cells could not previously be stacked because the individual cells could not be isolated.

“Before, if you joined several memory cells together you wouldn’t be able to access one without accessing all of the others because they were all wired together,” Kozicki explained. “What we did was put in an access, or islolation device, that electrically splits all of them into individual cells.”

Each memory cell has a built-in diode to isolate the layer, which will “allow us to put in as many layers as we can squeeze in there,” Kozicki said.

Each layer adds significantly more memory to the chip. For example, a chip with eight layers of memory would have nearly eight times as much capacity in the same area as a conventional single-layered chip.

“Stackable memory is thought to be the only way of reaching the densities necessary for the type of solid state memory that can compete with hard drives on cost as well as information capacity,” he said. “It turns out to be a ridiculously simple idea, but it works. It works better than the complicated ideas work.”

Moore’s Law, which stipulates that computer power will double approximately every 18 months, seems to be in effect for some time to come.

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