Houston (ip-192.com): Hynix Semiconductor Inc. and Hewlett-Packard Co. agreed to develop a new kind of universal memory dubbed “ReRam” or Resistive Random Access Memory to eventually replace DRAM or dynamic random access memory and flash memory. ReRam is based on a technology known as memory resistor, or memristor, that consists of passive two-terminal circuit elements that maintain a functional relationship between current and voltage. It allows a greater data density than current hard drives with access times similar or faster than achieved by today’s DRAM.
Only two years ago, HP researchers showed that memristors can act both as computers and memory. Now researchers from Rice University reported that nanotubes made from silicon dioxide, one of the most common chemical compounds on earth, can repeatedly break and reconnect its crystal structure when a current is applied. This behavior can be used to store information in nanocrystal tubes that are on a microscopic scale.
Jun Yao, a graduate student in Tour's lab and primary author of a paper that just appeared in the online edition of Nano Letters, confirmed his breakthrough idea when he sandwiched a layer of silicon oxide, an insulator, between semiconducting sheets of polycrystalline silicon that served as the top and bottom electrodes.
Applying a charge to the electrodes created a conductive pathway by stripping oxygen atoms from the silicon oxide and forming a chain of nano-sized silicon crystals. Once formed, the chain can be repeatedly broken and reconnected by applying a pulse of varying voltage.
The team was able to stack nanotubes, creating 3 D structures that can function as memory. “I would argue the nanowire-based solution is much more amenable to vertical stacking, which makes the technology very scalable as process technology improves,” said Lin Zhong, a professor at Rice University. “The density can be further doubled or tripled with two or three layers.”
The nanocrystal tubes or wirers are only 5 nanometers wide. While NAND flash memory is controlled by three wirers, the new silicon based memory only requires two terminals. This makes it possible to create three-dimensional stacks.
The beauty of it is its simplicity," said James Tour, a professor of mechanical engineering and materials and computer science, in a press release. That, he said, will be key to the technology's scalability. Silicon-oxide memories are compatible with conventional transistor manufacturing technology, said Tour, who recently attended a workshop by the National Science Foundation and IBM on breaking the barriers to Moore's Law, which states the number of devices on a circuit doubles every 18 to 24 months.
"Manufacturers feel they can get pathways down to 10 nanometers," Tour said. "Flash memory is going to hit a brick wall at about 20 nanometers. But how do we get beyond that? Well, our technique is perfectly suited for sub-10-nanometer circuits."
PrivaTran, an Austin, Texas based tech design company, is already bench testing a silicon-oxide chip with 1,000 memory elements built in collaboration with the Tour lab. "We're real excited about where the data is going here," said PrivaTran CEO Glenn Mortland, who is using the technology in several projects supported by the Army Research Office, National Science Foundation, Air Force Office of Scientific Research, and the Navy Space and Naval Warfare Systems Command Small Business Innovation Research (SBIR) and Small Business Technology Transfer programs. "Our original customer funding was geared toward more high-density memories. That's where most of the paying customers see this going. I think, along the way, there will be side applications in various nonvolatile configurations."
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