Researchers have invented a dual-mode device that can act as both volatile and nonvolatile memory.  (Source: NCSU via IEEE)

They actually have made a rough working prototype of the device.  (Source: NCSU via IEEE)
Volatile storage, meet nonvolatile storage

Scientists have created a new device that can offer both dynamic and long-term storage and could revolutionize the field of electronics.  Where current devices have separate memory and storage chips, future devices could rely on a single bank of homogenous chips.

Traditionally, (volatile) memory and storage are separate entities on modern computers.  The volatile memory involves chips with very fast access times that must be powered to retain information.  Often the term "memory" is used synonymously with the longer phrase volatile memory.  It's typically used to store details about the running programs.  By contrast storage (nonvolatile memory) offers slower access times, but can hold information even after a circuit is powered off.

If you've ever looked at a NAND flash storage cell (nonvolatile) and a DRAM cell (volatile), you'll realize that long-term and short-term storage don't necessarily have to be dramatically different in structure.

Perhaps that was the inspiration of North Carolina State University, which has invented a new device dubbed the dual floating gate field effect transistor cell (DFG-FET), which packs both devices into a single cell.  The DFG-FET consists of the two FET gates separated from each other by an insulating layer of silicon oxide.  Above the top FET rests a control gate, which can change the state of transistors by applying different voltages.

As a RAM cell, the two-transistor device has a read time of 0.31-2.18 ns (similar to SDRAM and faster than DRAM), a 50 ns write time for the charged state ('1'), and a 10 µs write time for the uncharged ('0') state.  Non-volatile writes range from 10 to 30 µs.

The device can tell what mode the current command is, based on the individual voltages provided to the gate transistors via the word line (WL) and select line (SL).

Dr. Paul Franzon, a professor of electrical and computer engineering at NC State and co-author of the paper on the work, states [press release], "We've invented a new device that may revolutionize computer memory."

Possible applications in the short term include unified memory for server farms.  Currently, server farms can't turn off specific servers to save power, as they would lose the information stored in their volatile memory.  As the new device operates faster, it could quickly cache the current volatile memory state in free non-volatile memory and then power off, quickly retrieving it when powered back on.  

Aside from server power savings, the paper shows off an FPGA circuit that could offer both space and power savings over current designs.  FPGAs are reprogrammable hardware chips (think a CPU which could be switched from an ARM architecture to a x86 architecture by flashing the chip), which are increasingly seeing use in a variety of devices.

And the researchers propose that the device could be used to create "instant on" computers and portable electronic devices, which didn't require lengthy boot times (which have even crept into the smartphone space).

The paper on the exciting new device is published [abstract] in the IEEE journal Computer.  The study was funded by a National Science Foundation grant.  Co-authors of the paper included former NC State Ph.D. student Daniel Schinke; former NC State master's student Mihir Shiveshwarkar; and Dr. Neil Di Spigna, a research assistant professor at NC State.

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